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 $67.82   13.718%   $77.1235   $77.12   $77.10   $77.10  
  Purchase #2 $48.46   13.832%   $55.163   $55.16   $55.15   $55.20  
  Purchase #3 $5.33   7.150%   $5.7111   $5.71   $5.70   $5.70  
  Purchase #4 $137.39   7.682%   $147.9443   $147.94   $147.95   $147.90  
  Purchase #5 $149.82   5.172%   $157.5687   $157.57   $157.55   $157.60  
  Purchase #6 $201.43   11.477%   $224.5481   $224.55   $224.55   $224.50  
  Purchase #7 $250.75   13.370%   $284.2753   $284.28   $284.30   $284.30  
  7 purchase totals = $861.00       $952.3340   $952.33   $952.30   $952.30