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 $55.60   10.122%   $61.2278   $61.23   $61.25   $61.20  
  Purchase #2 $14.86   8.454%   $16.1163   $16.12   $16.10   $16.10  
  Purchase #3 $112.39   9.202%   $122.7321   $122.73   $122.75   $122.70  
  Purchase #4 $66.58   8.158%   $72.0116   $72.01   $72.00   $72.00  
  Purchase #5 $53.94   10.585%   $59.6495   $59.65   $59.65   $59.60  
  Purchase #6 $136.58   10.112%   $150.391   $150.39   $150.40   $150.40  
  Purchase #7 $236.89   9.253%   $258.8094   $258.81   $258.80   $258.80  
  7 purchase totals = $676.84       $740.9377   $740.94   $740.95   $740.80