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 $43.83   13.627%   $49.8027   $49.80   $49.80   $49.80  
  Purchase #2 $146.37   10.338%   $161.5017   $161.50   $161.50   $161.50  
  Purchase #3 $111.92   5.664%   $118.2591   $118.26   $118.25   $118.30  
  Purchase #4 $237.72   4.118%   $247.5093   $247.51   $247.50   $247.50  
  Purchase #5 $75.73   6.359%   $80.5457   $80.55   $80.55   $80.50  
  Purchase #6 $105.82   5.525%   $111.6666   $111.67   $111.65   $111.70  
  Purchase #7 $244.80   5.679%   $258.7022   $258.70   $258.70   $258.70  
  7 purchase totals = $966.19       $1,027.9873   $1,027.99   $1,027.95   $1,028.00