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 $62.54   10.544%   $69.1342   $69.13   $69.15   $69.10  
  Purchase #2 $68.49   13.445%   $77.6985   $77.70   $77.70   $77.70  
  Purchase #3 $125.61   7.818%   $135.4302   $135.43   $135.45   $135.40  
  Purchase #4 $232.83   9.406%   $254.73   $254.73   $254.75   $254.70  
  Purchase #5 $137.53   13.659%   $156.3152   $156.32   $156.30   $156.30  
  Purchase #6 $140.79   7.278%   $151.0367   $151.04   $151.05   $151.00  
  Purchase #7 $130.49   4.727%   $136.6583   $136.66   $136.65   $136.70  
  7 purchase totals = $898.28       $981.0031   $981.01   $981.05   $980.90