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 $225.87   13.650%   $256.7013   $256.70   $256.70   $256.70  
  Purchase #2 $173.48   6.198%   $184.2323   $184.23   $184.25   $184.20  
  Purchase #3 $241.47   12.738%   $272.2284   $272.23   $272.25   $272.20  
  Purchase #4 $154.84   13.813%   $176.228   $176.23   $176.25   $176.20  
  Purchase #5 $62.36   7.334%   $66.9335   $66.93   $66.95   $66.90  
  Purchase #6 $182.54   8.213%   $197.532   $197.53   $197.55   $197.50  
  Purchase #7 $181.43   12.124%   $203.4266   $203.43   $203.45   $203.40  
  7 purchase totals = $1,221.99       $1,357.2821   $1,357.28   $1,357.40   $1,357.10