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 $244.45   13.410%   $277.2307   $277.23   $277.25   $277.20  
  Purchase #2 $30.34   7.295%   $32.5533   $32.55   $32.55   $32.60  
  Purchase #3 $184.30   9.695%   $202.1679   $202.17   $202.15   $202.20  
  Purchase #4 $58.66   11.824%   $65.596   $65.60   $65.60   $65.60  
  Purchase #5 $137.82   5.137%   $144.8998   $144.90   $144.90   $144.90  
  Purchase #6 $66.38   4.851%   $69.6001   $69.60   $69.60   $69.60  
  Purchase #7 $203.56   7.730%   $219.2952   $219.30   $219.30   $219.30  
  7 purchase totals = $925.51       $1,011.3430   $1,011.35   $1,011.35   $1,011.40