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 $59.99   9.205%   $65.5121   $65.51   $65.50   $65.50  
  Purchase #2 $40.86   12.252%   $45.8662   $45.87   $45.85   $45.90  
  Purchase #3 $219.28   8.526%   $237.9758   $237.98   $238.00   $238.00  
  Purchase #4 $228.93   5.134%   $240.6833   $240.68   $240.70   $240.70  
  Purchase #5 $127.45   12.595%   $143.5023   $143.50   $143.50   $143.50  
  Purchase #6 $172.57   12.416%   $193.9963   $194.00   $194.00   $194.00  
  Purchase #7 $72.96   5.485%   $76.9619   $76.96   $76.95   $77.00  
  7 purchase totals = $922.04       $1,004.4979   $1,004.50   $1,004.50   $1,004.60