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 $66.76   7.779%   $71.9533   $71.95   $71.95   $72.00  
  Purchase #2 $223.58   13.311%   $253.3407   $253.34   $253.35   $253.30  
  Purchase #3 $233.28   10.711%   $258.2666   $258.27   $258.25   $258.30  
  Purchase #4 $178.82   3.232%   $184.5995   $184.60   $184.60   $184.60  
  Purchase #5 $166.59   6.482%   $177.3884   $177.39   $177.40   $177.40  
  Purchase #6 $231.67   5.699%   $244.8729   $244.87   $244.85   $244.90  
  Purchase #7 $69.90   11.250%   $77.7638   $77.76   $77.75   $77.80  
  7 purchase totals = $1,170.60       $1,268.1852   $1,268.18   $1,268.15   $1,268.30