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 $235.61   8.740%   $256.2023   $256.20   $256.20   $256.20  
  Purchase #2 $149.96   8.557%   $162.7921   $162.79   $162.80   $162.80  
  Purchase #3 $115.49   3.494%   $119.5252   $119.53   $119.55   $119.50  
  Purchase #4 $102.49   5.706%   $108.3381   $108.34   $108.35   $108.30  
  Purchase #5 $220.29   12.726%   $248.3241   $248.32   $248.30   $248.30  
  Purchase #6 $95.72   11.794%   $107.0092   $107.01   $107.00   $107.00  
  Purchase #7 $197.38   8.736%   $214.6231   $214.62   $214.60   $214.60  
  7 purchase totals = $1,116.94       $1,216.8141   $1,216.81   $1,216.80   $1,216.70