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 $48.49   9.847%   $53.2648   $53.26   $53.25   $53.30  
  Purchase #2 $213.39   12.163%   $239.3446   $239.34   $239.35   $239.30  
  Purchase #3 $192.45   6.715%   $205.373   $205.37   $205.35   $205.40  
  Purchase #4 $227.88   13.158%   $257.8645   $257.86   $257.85   $257.90  
  Purchase #5 $219.81   3.134%   $226.6988   $226.70   $226.70   $226.70  
  Purchase #6 $116.99   12.200%   $131.2628   $131.26   $131.25   $131.30  
  Purchase #7 $121.36   12.399%   $136.4074   $136.41   $136.40   $136.40  
  7 purchase totals = $1,140.37       $1,250.2159   $1,250.20   $1,250.15   $1,250.30