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 $88.72   10.836%   $98.3337   $98.33   $98.35   $98.30  
  Purchase #2 $236.82   11.281%   $263.5357   $263.54   $263.55   $263.50  
  Purchase #3 $213.78   5.266%   $225.0377   $225.04   $225.05   $225.00  
  Purchase #4 $246.46   7.324%   $264.5107   $264.51   $264.50   $264.50  
  Purchase #5 $156.33   10.121%   $172.1522   $172.15   $172.15   $172.20  
  Purchase #6 $163.85   8.572%   $177.8952   $177.90   $177.90   $177.90  
  Purchase #7 $107.79   10.204%   $118.7889   $118.79   $118.80   $118.80  
  7 purchase totals = $1,213.75       $1,320.2541   $1,320.26   $1,320.30   $1,320.20