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 $205.91   7.621%   $221.6024   $221.60   $221.60   $221.60  
  Purchase #2 $248.30   7.114%   $265.9641   $265.96   $265.95   $266.00  
  Purchase #3 $172.78   4.685%   $180.8747   $180.87   $180.85   $180.90  
  Purchase #4 $65.58   6.657%   $69.9457   $69.95   $69.95   $69.90  
  Purchase #5 $107.35   10.201%   $118.3008   $118.30   $118.30   $118.30  
  Purchase #6 $160.73   12.542%   $180.8888   $180.89   $180.90   $180.90  
  Purchase #7 $166.93   6.227%   $177.3247   $177.32   $177.30   $177.30  
  7 purchase totals = $1,127.58       $1,214.9012   $1,214.89   $1,214.85   $1,214.90