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 $60.73   13.668%   $69.0306   $69.03   $69.05   $69.00  
  Purchase #2 $68.66   7.576%   $73.8617   $73.86   $73.85   $73.90  
  Purchase #3 $112.50   13.494%   $127.6808   $127.68   $127.70   $127.70  
  Purchase #4 $103.92   13.672%   $118.1279   $118.13   $118.15   $118.10  
  Purchase #5 $19.62   6.164%   $20.8294   $20.83   $20.85   $20.80  
  Purchase #6 $169.79   13.130%   $192.0834   $192.08   $192.10   $192.10  
  Purchase #7 $238.61   9.596%   $261.507   $261.51   $261.50   $261.50  
  7 purchase totals = $773.83       $863.1208   $863.12   $863.20   $863.10