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 $218.90   6.772%   $233.7239   $233.72   $233.70   $233.70  
  Purchase #2 $239.29   7.295%   $256.7462   $256.75   $256.75   $256.70  
  Purchase #3 $59.66   12.524%   $67.1318   $67.13   $67.15   $67.10  
  Purchase #4 $87.94   9.119%   $95.9592   $95.96   $95.95   $96.00  
  Purchase #5 $85.46   8.423%   $92.6583   $92.66   $92.65   $92.70  
  Purchase #6 $33.99   4.257%   $35.437   $35.44   $35.45   $35.40  
  Purchase #7 $25.75   4.462%   $26.899   $26.90   $26.90   $26.90  
  7 purchase totals = $750.99       $808.5554   $808.56   $808.55   $808.50