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 $54.80   7.723%   $59.0322   $59.03   $59.05   $59.00  
  Purchase #2 $72.99   13.778%   $83.0466   $83.05   $83.05   $83.00  
  Purchase #3 $212.78   5.799%   $225.1191   $225.12   $225.10   $225.10  
  Purchase #4 $61.77   6.259%   $65.6362   $65.64   $65.65   $65.60  
  Purchase #5 $232.80   6.227%   $247.2965   $247.30   $247.30   $247.30  
  Purchase #6 $52.66   10.658%   $58.2725   $58.27   $58.25   $58.30  
  Purchase #7 $72.45   5.514%   $76.4449   $76.44   $76.45   $76.40  
  7 purchase totals = $760.25       $814.8480   $814.85   $814.85   $814.70