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 $94.94   10.324%   $104.7416   $104.74   $104.75   $104.70  
  Purchase #2 $32.94   5.637%   $34.7968   $34.80   $34.80   $34.80  
  Purchase #3 $232.59   5.331%   $244.9894   $244.99   $245.00   $245.00  
  Purchase #4 $222.79   7.858%   $240.2968   $240.30   $240.30   $240.30  
  Purchase #5 $85.80   10.558%   $94.8588   $94.86   $94.85   $94.90  
  Purchase #6 $247.39   5.870%   $261.9118   $261.91   $261.90   $261.90  
  Purchase #7 $48.35   5.584%   $51.0499   $51.05   $51.05   $51.00  
  7 purchase totals = $964.80       $1,032.6451   $1,032.65   $1,032.65   $1,032.60