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 $60.89   12.390%   $68.4343   $68.43   $68.45   $68.40  
  Purchase #2 $173.45   8.197%   $187.6677   $187.67   $187.65   $187.70  
  Purchase #3 $237.97   13.846%   $270.9193   $270.92   $270.90   $270.90  
  Purchase #4 $113.27   9.114%   $123.5934   $123.59   $123.60   $123.60  
  Purchase #5 $182.53   13.118%   $206.4743   $206.47   $206.45   $206.50  
  Purchase #6 $110.81   9.827%   $121.6993   $121.70   $121.70   $121.70  
  Purchase #7 $97.40   10.451%   $107.5793   $107.58   $107.60   $107.60  
  7 purchase totals = $976.32       $1,086.3676   $1,086.36   $1,086.35   $1,086.40