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 $227.74   6.140%   $241.7232   $241.72   $241.70   $241.70  
  Purchase #2 $158.51   8.386%   $171.8026   $171.80   $171.80   $171.80  
  Purchase #3 $185.53   5.539%   $195.8065   $195.81   $195.80   $195.80  
  Purchase #4 $16.47   12.436%   $18.5182   $18.52   $18.50   $18.50  
  Purchase #5 $69.95   6.618%   $74.5793   $74.58   $74.60   $74.60  
  Purchase #6 $25.54   3.559%   $26.449   $26.45   $26.45   $26.40  
  Purchase #7 $30.87   8.501%   $33.4943   $33.49   $33.50   $33.50  
  7 purchase totals = $714.61       $762.3731   $762.37   $762.35   $762.30