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 $108.52   10.196%   $119.5847   $119.58   $119.60   $119.60  
  Purchase #2 $26.39   12.667%   $29.7328   $29.73   $29.75   $29.70  
  Purchase #3 $15.53   11.151%   $17.2618   $17.26   $17.25   $17.30  
  Purchase #4 $48.32   12.190%   $54.2102   $54.21   $54.20   $54.20  
  Purchase #5 $169.25   3.839%   $175.7475   $175.75   $175.75   $175.70  
  Purchase #6 $191.85   6.127%   $203.6046   $203.60   $203.60   $203.60  
  Purchase #7 $195.50   8.738%   $212.5828   $212.58   $212.60   $212.60  
  7 purchase totals = $755.36       $812.7244   $812.71   $812.75   $812.70