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 $58.90   13.118%   $66.6265   $66.63   $66.65   $66.60  
  Purchase #2 $188.89   4.593%   $197.5657   $197.57   $197.55   $197.60  
  Purchase #3 $132.46   12.809%   $149.4268   $149.43   $149.45   $149.40  
  Purchase #4 $156.76   6.104%   $166.3286   $166.33   $166.35   $166.30  
  Purchase #5 $135.97   11.327%   $151.3713   $151.37   $151.35   $151.40  
  Purchase #6 $108.76   6.137%   $115.4346   $115.43   $115.45   $115.40  
  Purchase #7 $153.68   3.762%   $159.4614   $159.46   $159.45   $159.50  
  7 purchase totals = $935.42       $1,006.2149   $1,006.22   $1,006.25   $1,006.20