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 $209.44   12.551%   $235.7268   $235.73   $235.75   $235.70  
  Purchase #2 $14.98   8.665%   $16.278   $16.28   $16.30   $16.30  
  Purchase #3 $200.93   9.283%   $219.5823   $219.58   $219.60   $219.60  
  Purchase #4 $22.76   8.709%   $24.7422   $24.74   $24.75   $24.70  
  Purchase #5 $46.40   11.192%   $51.5931   $51.59   $51.60   $51.60  
  Purchase #6 $189.66   6.749%   $202.4602   $202.46   $202.45   $202.50  
  Purchase #7 $13.80   7.293%   $14.8064   $14.81   $14.80   $14.80  
  7 purchase totals = $697.97       $765.1890   $765.19   $765.25   $765.20