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 $189.86   12.778%   $214.1203   $214.12   $214.10   $214.10  
  Purchase #2 $157.58   3.799%   $163.5665   $163.57   $163.55   $163.60  
  Purchase #3 $164.49   3.205%   $169.7619   $169.76   $169.75   $169.80  
  Purchase #4 $213.26   13.435%   $241.9115   $241.91   $241.90   $241.90  
  Purchase #5 $143.59   6.114%   $152.3691   $152.37   $152.35   $152.40  
  Purchase #6 $62.90   11.184%   $69.9347   $69.93   $69.95   $69.90  
  Purchase #7 $22.49   8.251%   $24.3456   $24.35   $24.35   $24.30  
  7 purchase totals = $954.17       $1,036.0096   $1,036.01   $1,035.95   $1,036.00