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 $83.35   11.106%   $92.6069   $92.61   $92.60   $92.60  
  Purchase #2 $162.85   7.746%   $175.4644   $175.46   $175.45   $175.50  
  Purchase #3 $119.47   6.668%   $127.4363   $127.44   $127.45   $127.40  
  Purchase #4 $247.60   6.453%   $263.5776   $263.58   $263.60   $263.60  
  Purchase #5 $12.31   4.239%   $12.8318   $12.83   $12.85   $12.80  
  Purchase #6 $199.38   5.306%   $209.9591   $209.96   $209.95   $210.00  
  Purchase #7 $14.28   6.651%   $15.2298   $15.23   $15.25   $15.20  
  7 purchase totals = $839.24       $897.1059   $897.11   $897.15   $897.10