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 $58.66   9.742%   $64.3747   $64.37   $64.35   $64.40  
  Purchase #2 $131.60   3.828%   $136.6376   $136.64   $136.65   $136.60  
  Purchase #3 $174.30   13.570%   $197.9525   $197.95   $197.95   $198.00  
  Purchase #4 $56.98   7.698%   $61.3663   $61.37   $61.35   $61.40  
  Purchase #5 $192.43   5.480%   $202.9752   $202.98   $203.00   $203.00  
  Purchase #6 $61.56   3.686%   $63.8291   $63.83   $63.85   $63.80  
  Purchase #7 $127.95   10.177%   $140.9715   $140.97   $140.95   $141.00  
  7 purchase totals = $803.48       $868.1069   $868.11   $868.10   $868.20