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 $87.28   12.251%   $97.9727   $97.97   $97.95   $98.00  
  Purchase #2 $135.43   3.788%   $140.5601   $140.56   $140.55   $140.60  
  Purchase #3 $42.50   7.799%   $45.8146   $45.81   $45.80   $45.80  
  Purchase #4 $32.34   3.286%   $33.4027   $33.40   $33.40   $33.40  
  Purchase #5 $192.63   11.191%   $214.1872   $214.19   $214.20   $214.20  
  Purchase #6 $212.53   13.481%   $241.1812   $241.18   $241.20   $241.20  
  Purchase #7 $171.83   7.402%   $184.5489   $184.55   $184.55   $184.50  
  7 purchase totals = $874.54       $957.6674   $957.66   $957.65   $957.70