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 $58.33   9.752%   $64.0183   $64.02   $64.00   $64.00  
  Purchase #2 $230.65   9.148%   $251.7499   $251.75   $251.75   $251.70  
  Purchase #3 $64.62   6.416%   $68.766   $68.77   $68.75   $68.80  
  Purchase #4 $206.49   8.107%   $223.2301   $223.23   $223.25   $223.20  
  Purchase #5 $43.84   8.140%   $47.4086   $47.41   $47.40   $47.40  
  Purchase #6 $56.61   4.352%   $59.0737   $59.07   $59.05   $59.10  
  Purchase #7 $236.49   4.464%   $247.0469   $247.05   $247.05   $247.00  
  7 purchase totals = $897.03       $961.2935   $961.30   $961.25   $961.20