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 $244.81   8.264%   $265.0411   $265.04   $265.05   $265.00  
  Purchase #2 $106.35   12.801%   $119.9639   $119.96   $119.95   $120.00  
  Purchase #3 $170.70   10.289%   $188.2633   $188.26   $188.25   $188.30  
  Purchase #4 $232.98   10.753%   $258.0323   $258.03   $258.05   $258.00  
  Purchase #5 $168.82   8.736%   $183.5681   $183.57   $183.55   $183.60  
  Purchase #6 $29.36   4.417%   $30.6568   $30.66   $30.65   $30.70  
  Purchase #7 $109.64   10.102%   $120.7158   $120.72   $120.70   $120.70  
  7 purchase totals = $1,062.66       $1,166.2413   $1,166.24   $1,166.20   $1,166.30