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 $82.64   13.269%   $93.6055   $93.61   $93.60   $93.60  
  Purchase #2 $144.38   8.758%   $157.0248   $157.02   $157.00   $157.00  
  Purchase #3 $8.77   12.636%   $9.8782   $9.88   $9.90   $9.90  
  Purchase #4 $203.74   12.815%   $229.8493   $229.85   $229.85   $229.80  
  Purchase #5 $106.85   11.702%   $119.3536   $119.35   $119.35   $119.40  
  Purchase #6 $230.46   10.867%   $255.5041   $255.50   $255.50   $255.50  
  Purchase #7 $39.76   12.572%   $44.7586   $44.76   $44.75   $44.80  
  7 purchase totals = $816.60       $909.9741   $909.97   $909.95   $910.00