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 $224.96   13.226%   $254.7132   $254.71   $254.70   $254.70  
  Purchase #2 $155.85   5.343%   $164.1771   $164.18   $164.20   $164.20  
  Purchase #3 $140.29   12.215%   $157.4264   $157.43   $157.45   $157.40  
  Purchase #4 $182.67   11.682%   $204.0095   $204.01   $204.00   $204.00  
  Purchase #5 $61.62   5.820%   $65.2063   $65.21   $65.20   $65.20  
  Purchase #6 $217.49   11.258%   $241.975   $241.98   $242.00   $242.00  
  Purchase #7 $39.99   5.505%   $42.1914   $42.19   $42.20   $42.20  
  7 purchase totals = $1,022.87       $1,129.6989   $1,129.71   $1,129.75   $1,129.70