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 $59.35   7.159%   $63.5989   $63.60   $63.60   $63.60  
  Purchase #2 $204.34   11.408%   $227.6511   $227.65   $227.65   $227.70  
  Purchase #3 $221.45   13.650%   $251.6779   $251.68   $251.70   $251.70  
  Purchase #4 $175.55   6.811%   $187.5067   $187.51   $187.50   $187.50  
  Purchase #5 $94.36   10.223%   $104.0064   $104.01   $104.00   $104.00  
  Purchase #6 $58.89   7.830%   $63.5011   $63.50   $63.50   $63.50  
  Purchase #7 $169.98   10.740%   $188.2359   $188.24   $188.25   $188.20  
  7 purchase totals = $983.92       $1,086.1780   $1,086.19   $1,086.20   $1,086.20