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 $220.99   5.425%   $232.9787   $232.98   $233.00   $233.00  
  Purchase #2 $65.95   6.407%   $70.1754   $70.18   $70.20   $70.20  
  Purchase #3 $238.43   11.112%   $264.9243   $264.92   $264.90   $264.90  
  Purchase #4 $207.91   10.227%   $229.173   $229.17   $229.15   $229.20  
  Purchase #5 $170.45   6.802%   $182.044   $182.04   $182.05   $182.00  
  Purchase #6 $119.94   13.254%   $135.8368   $135.84   $135.85   $135.80  
  Purchase #7 $221.44   6.398%   $235.6077   $235.61   $235.60   $235.60  
  7 purchase totals = $1,245.11       $1,350.7399   $1,350.74   $1,350.75   $1,350.70