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 $197.82   13.856%   $225.2299   $225.23   $225.25   $225.20  
  Purchase #2 $137.76   11.334%   $153.3737   $153.37   $153.35   $153.40  
  Purchase #3 $83.65   13.264%   $94.7453   $94.75   $94.75   $94.70  
  Purchase #4 $39.49   8.239%   $42.7436   $42.74   $42.75   $42.70  
  Purchase #5 $150.49   6.397%   $160.1168   $160.12   $160.10   $160.10  
  Purchase #6 $183.47   12.365%   $206.1561   $206.16   $206.15   $206.20  
  Purchase #7 $193.48   10.133%   $213.0853   $213.09   $213.10   $213.10  
  7 purchase totals = $986.16       $1,095.4507   $1,095.46   $1,095.45   $1,095.40