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 $244.96   6.401%   $260.6399   $260.64   $260.65   $260.60  
  Purchase #2 $58.79   5.493%   $62.0193   $62.02   $62.00   $62.00  
  Purchase #3 $12.25   6.578%   $13.0558   $13.06   $13.05   $13.10  
  Purchase #4 $28.65   11.452%   $31.931   $31.93   $31.95   $31.90  
  Purchase #5 $199.74   8.567%   $216.8517   $216.85   $216.85   $216.90  
  Purchase #6 $169.53   11.649%   $189.2785   $189.28   $189.30   $189.30  
  Purchase #7 $189.37   5.493%   $199.7721   $199.77   $199.75   $199.80  
  7 purchase totals = $903.29       $973.5483   $973.55   $973.55   $973.60