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 $54.49   11.275%   $60.6337   $60.63   $60.65   $60.60  
  Purchase #2 $177.53   4.373%   $185.2934   $185.29   $185.30   $185.30  
  Purchase #3 $109.82   13.380%   $124.5139   $124.51   $124.50   $124.50  
  Purchase #4 $73.26   6.155%   $77.7692   $77.77   $77.75   $77.80  
  Purchase #5 $25.99   5.166%   $27.3326   $27.33   $27.35   $27.30  
  Purchase #6 $199.58   13.485%   $226.4934   $226.49   $226.50   $226.50  
  Purchase #7 $140.54   7.500%   $151.0805   $151.08   $151.10   $151.10  
  7 purchase totals = $781.21       $853.1167   $853.10   $853.15   $853.10