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 $127.26   11.351%   $141.7053   $141.71   $141.70   $141.70  
  Purchase #2 $233.83   9.871%   $256.9114   $256.91   $256.90   $256.90  
  Purchase #3 $5.31   3.470%   $5.4943   $5.49   $5.50   $5.50  
  Purchase #4 $219.57   8.163%   $237.4935   $237.49   $237.50   $237.50  
  Purchase #5 $91.62   5.568%   $96.7214   $96.72   $96.70   $96.70  
  Purchase #6 $210.51   13.802%   $239.5646   $239.56   $239.55   $239.60  
  Purchase #7 $227.62   5.858%   $240.954   $240.95   $240.95   $241.00  
  7 purchase totals = $1,115.72       $1,218.8445   $1,218.83   $1,218.80   $1,218.90