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 $238.33   10.198%   $262.6349   $262.63   $262.65   $262.60  
  Purchase #2 $84.82   12.337%   $95.2842   $95.28   $95.30   $95.30  
  Purchase #3 $193.31   8.701%   $210.1299   $210.13   $210.15   $210.10  
  Purchase #4 $85.54   7.424%   $91.8905   $91.89   $91.90   $91.90  
  Purchase #5 $85.25   6.217%   $90.55   $90.55   $90.55   $90.60  
  Purchase #6 $29.63   7.762%   $31.9299   $31.93   $31.95   $31.90  
  Purchase #7 $103.97   9.400%   $113.7432   $113.74   $113.75   $113.70  
  7 purchase totals = $820.85       $896.1626   $896.15   $896.25   $896.10