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 $87.37   8.510%   $94.8052   $94.81   $94.80   $94.80  
  Purchase #2 $166.57   11.305%   $185.4007   $185.40   $185.40   $185.40  
  Purchase #3 $164.57   8.323%   $178.2672   $178.27   $178.25   $178.30  
  Purchase #4 $140.52   10.436%   $155.1847   $155.18   $155.20   $155.20  
  Purchase #5 $113.73   9.277%   $124.2807   $124.28   $124.30   $124.30  
  Purchase #6 $131.53   8.833%   $143.148   $143.15   $143.15   $143.10  
  Purchase #7 $74.50   6.605%   $79.4207   $79.42   $79.40   $79.40  
  7 purchase totals = $878.79       $960.5072   $960.51   $960.50   $960.50