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 $213.26   11.613%   $238.0259   $238.03   $238.05   $238.00  
  Purchase #2 $171.40   10.243%   $188.9565   $188.96   $188.95   $189.00  
  Purchase #3 $229.56   9.605%   $251.6092   $251.61   $251.60   $251.60  
  Purchase #4 $120.59   3.134%   $124.3693   $124.37   $124.35   $124.40  
  Purchase #5 $231.31   13.385%   $262.2708   $262.27   $262.25   $262.30  
  Purchase #6 $217.68   9.519%   $238.401   $238.40   $238.40   $238.40  
  Purchase #7 $37.92   8.567%   $41.1686   $41.17   $41.15   $41.20  
  7 purchase totals = $1,221.72       $1,344.8013   $1,344.81   $1,344.75   $1,344.90