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 $36.65   12.719%   $41.3115   $41.31   $41.30   $41.30  
  Purchase #2 $246.75   9.700%   $270.6848   $270.68   $270.70   $270.70  
  Purchase #3 $54.67   5.352%   $57.5959   $57.60   $57.60   $57.60  
  Purchase #4 $159.40   4.491%   $166.5587   $166.56   $166.55   $166.60  
  Purchase #5 $194.26   8.228%   $210.2437   $210.24   $210.25   $210.20  
  Purchase #6 $140.43   3.714%   $145.6456   $145.65   $145.65   $145.60  
  Purchase #7 $143.95   5.450%   $151.7953   $151.80   $151.80   $151.80  
  7 purchase totals = $976.11       $1,043.8355   $1,043.84   $1,043.85   $1,043.80