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 $94.83   9.593%   $103.927   $103.93   $103.95   $103.90  
  Purchase #2 $22.66   11.838%   $25.3425   $25.34   $25.35   $25.30  
  Purchase #3 $161.29   5.112%   $169.5351   $169.54   $169.55   $169.50  
  Purchase #4 $240.65   13.462%   $273.0463   $273.05   $273.05   $273.00  
  Purchase #5 $68.79   12.441%   $77.3482   $77.35   $77.35   $77.30  
  Purchase #6 $205.76   11.841%   $230.124   $230.12   $230.10   $230.10  
  Purchase #7 $148.69   4.610%   $155.5446   $155.54   $155.55   $155.50  
  7 purchase totals = $942.67       $1,034.8677   $1,034.87   $1,034.90   $1,034.60