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 $141.84   3.126%   $146.2739   $146.27   $146.25   $146.30  
  Purchase #2 $150.53   12.668%   $169.5991   $169.60   $169.60   $169.60  
  Purchase #3 $187.43   3.419%   $193.8382   $193.84   $193.85   $193.80  
  Purchase #4 $192.93   8.819%   $209.9445   $209.94   $209.95   $209.90  
  Purchase #5 $165.56   6.763%   $176.7568   $176.76   $176.75   $176.80  
  Purchase #6 $119.51   10.465%   $132.0167   $132.02   $132.00   $132.00  
  Purchase #7 $245.31   4.345%   $255.9687   $255.97   $255.95   $256.00  
  7 purchase totals = $1,203.11       $1,284.3979   $1,284.40   $1,284.35   $1,284.40