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 $171.82   6.352%   $182.734   $182.73   $182.75   $182.70  
  Purchase #2 $85.80   12.355%   $96.4006   $96.40   $96.40   $96.40  
  Purchase #3 $183.79   12.532%   $206.8226   $206.82   $206.80   $206.80  
  Purchase #4 $55.81   12.785%   $62.9453   $62.95   $62.95   $62.90  
  Purchase #5 $35.82   5.461%   $37.7761   $37.78   $37.80   $37.80  
  Purchase #6 $245.82   9.802%   $269.9153   $269.92   $269.90   $269.90  
  Purchase #7 $163.25   3.681%   $169.2592   $169.26   $169.25   $169.30  
  7 purchase totals = $942.11       $1,025.8531   $1,025.86   $1,025.85   $1,025.80