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 $48.96   4.468%   $51.1475   $51.15   $51.15   $51.10  
  Purchase #2 $173.81   13.495%   $197.2657   $197.27   $197.25   $197.30  
  Purchase #3 $82.53   6.149%   $87.6048   $87.60   $87.60   $87.60  
  Purchase #4 $225.37   12.245%   $252.9666   $252.97   $252.95   $253.00  
  Purchase #5 $50.92   5.418%   $53.6788   $53.68   $53.70   $53.70  
  Purchase #6 $195.63   12.516%   $220.1151   $220.12   $220.10   $220.10  
  Purchase #7 $131.32   8.704%   $142.7501   $142.75   $142.75   $142.80  
  7 purchase totals = $908.54       $1,005.5286   $1,005.54   $1,005.50   $1,005.60