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 $53.76   13.833%   $61.1966   $61.20   $61.20   $61.20  
  Purchase #2 $228.41   8.267%   $247.2927   $247.29   $247.30   $247.30  
  Purchase #3 $89.74   7.700%   $96.65   $96.65   $96.65   $96.70  
  Purchase #4 $6.69   7.319%   $7.1796   $7.18   $7.20   $7.20  
  Purchase #5 $64.25   11.262%   $71.4858   $71.49   $71.50   $71.50  
  Purchase #6 $79.78   12.847%   $90.0293   $90.03   $90.05   $90.00  
  Purchase #7 $215.37   13.752%   $244.9877   $244.99   $245.00   $245.00  
  7 purchase totals = $738.00       $818.8217   $818.83   $818.90   $818.90