Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $102.71   3.183%   $105.9793   $105.98   $106.00   $106.00  
  Purchase #2 $132.92   6.420%   $141.4535   $141.45   $141.45   $141.50  
  Purchase #3 $91.83   9.173%   $100.2536   $100.25   $100.25   $100.30  
  Purchase #4 $223.37   7.221%   $239.4995   $239.50   $239.50   $239.50  
  Purchase #5 $169.74   12.638%   $191.1917   $191.19   $191.20   $191.20  
  Purchase #6 $237.99   4.705%   $249.1874   $249.19   $249.20   $249.20  
  Purchase #7 $117.68   6.352%   $125.155   $125.16   $125.15   $125.20  
  7 purchase totals = $1,076.24       $1,152.7200   $1,152.72   $1,152.75   $1,152.90