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 $44.67   10.134%   $49.1969   $49.20   $49.20   $49.20  
  Purchase #2 $148.96   13.668%   $169.3199   $169.32   $169.30   $169.30  
  Purchase #3 $76.25   4.816%   $79.9222   $79.92   $79.90   $79.90  
  Purchase #4 $126.95   9.165%   $138.585   $138.59   $138.60   $138.60  
  Purchase #5 $126.91   3.544%   $131.4077   $131.41   $131.40   $131.40  
  Purchase #6 $157.46   8.633%   $171.0535   $171.05   $171.05   $171.10  
  Purchase #7 $33.36   5.752%   $35.2789   $35.28   $35.30   $35.30  
  7 purchase totals = $714.56       $774.7641   $774.77   $774.75   $774.80