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 $53.58   9.408%   $58.6208   $58.62   $58.60   $58.60  
  Purchase #2 $166.37   4.803%   $174.3608   $174.36   $174.35   $174.40  
  Purchase #3 $184.70   8.120%   $199.6976   $199.70   $199.70   $199.70  
  Purchase #4 $92.57   4.659%   $96.8828   $96.88   $96.90   $96.90  
  Purchase #5 $162.95   6.152%   $172.9747   $172.97   $172.95   $173.00  
  Purchase #6 $108.68   3.613%   $112.6066   $112.61   $112.60   $112.60  
  Purchase #7 $116.75   11.374%   $130.0291   $130.03   $130.05   $130.00  
  7 purchase totals = $885.60       $945.1724   $945.17   $945.15   $945.20