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 $195.93   4.110%   $203.9827   $203.98   $204.00   $204.00  
  Purchase #2 $161.25   13.341%   $182.7624   $182.76   $182.75   $182.80  
  Purchase #3 $219.91   7.576%   $236.5704   $236.57   $236.55   $236.60  
  Purchase #4 $22.86   13.339%   $25.9093   $25.91   $25.90   $25.90  
  Purchase #5 $206.25   12.690%   $232.4231   $232.42   $232.40   $232.40  
  Purchase #6 $131.82   11.380%   $146.8211   $146.82   $146.80   $146.80  
  Purchase #7 $32.53   5.310%   $34.2573   $34.26   $34.25   $34.30  
  7 purchase totals = $970.55       $1,062.7263   $1,062.72   $1,062.65   $1,062.80