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 $207.76   6.242%   $220.7284   $220.73   $220.75   $220.70  
  Purchase #2 $100.95   13.866%   $114.9477   $114.95   $114.95   $114.90  
  Purchase #3 $74.68   12.211%   $83.7992   $83.80   $83.80   $83.80  
  Purchase #4 $163.33   5.674%   $172.5973   $172.60   $172.60   $172.60  
  Purchase #5 $221.78   5.415%   $233.7894   $233.79   $233.80   $233.80  
  Purchase #6 $39.72   11.206%   $44.171   $44.17   $44.15   $44.20  
  Purchase #7 $152.93   5.393%   $161.1775   $161.18   $161.20   $161.20  
  7 purchase totals = $961.15       $1,031.2105   $1,031.22   $1,031.25   $1,031.20