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 $48.31   12.406%   $54.3033   $54.30   $54.30   $54.30  
  Purchase #2 $42.44   11.700%   $47.4055   $47.41   $47.40   $47.40  
  Purchase #3 $84.95   12.815%   $95.8363   $95.84   $95.85   $95.80  
  Purchase #4 $203.51   13.786%   $231.5659   $231.57   $231.55   $231.60  
  Purchase #5 $249.61   10.372%   $275.4995   $275.50   $275.50   $275.50  
  Purchase #6 $59.47   4.874%   $62.3686   $62.37   $62.35   $62.40  
  Purchase #7 $224.73   4.568%   $234.9957   $235.00   $235.00   $235.00  
  7 purchase totals = $913.02       $1,001.9748   $1,001.99   $1,001.95   $1,002.00