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 $41.26   6.810%   $44.0698   $44.07   $44.05   $44.10  
  Purchase #2 $10.40   12.549%   $11.7051   $11.71   $11.70   $11.70  
  Purchase #3 $111.42   6.782%   $118.9765   $118.98   $119.00   $119.00  
  Purchase #4 $220.98   7.493%   $237.538   $237.54   $237.55   $237.50  
  Purchase #5 $185.54   4.551%   $193.9839   $193.98   $194.00   $194.00  
  Purchase #6 $167.44   13.179%   $189.5069   $189.51   $189.50   $189.50  
  Purchase #7 $72.73   10.137%   $80.1026   $80.10   $80.10   $80.10  
  7 purchase totals = $809.77       $875.8828   $875.89   $875.90   $875.90