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 $68.95   12.547%   $77.6012   $77.60   $77.60   $77.60  
  Purchase #2 $87.82   5.150%   $92.3427   $92.34   $92.35   $92.30  
  Purchase #3 $51.67   3.594%   $53.527   $53.53   $53.55   $53.50  
  Purchase #4 $77.80   10.143%   $85.6913   $85.69   $85.70   $85.70  
  Purchase #5 $152.72   6.810%   $163.1202   $163.12   $163.10   $163.10  
  Purchase #6 $190.33   5.238%   $200.2995   $200.30   $200.30   $200.30  
  Purchase #7 $236.34   9.445%   $258.6623   $258.66   $258.65   $258.70  
  7 purchase totals = $865.63       $931.2442   $931.24   $931.25   $931.20