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 $68.80   6.607%   $73.3456   $73.35   $73.35   $73.30  
  Purchase #2 $154.62   11.178%   $171.9034   $171.90   $171.90   $171.90  
  Purchase #3 $211.76   12.397%   $238.0119   $238.01   $238.00   $238.00  
  Purchase #4 $248.61   9.641%   $272.5785   $272.58   $272.60   $272.60  
  Purchase #5 $7.94   6.504%   $8.4564   $8.46   $8.45   $8.50  
  Purchase #6 $78.86   4.430%   $82.3535   $82.35   $82.35   $82.40  
  Purchase #7 $57.47   9.753%   $63.075   $63.08   $63.10   $63.10  
  7 purchase totals = $828.06       $909.7243   $909.73   $909.75   $909.80