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 $62.63   13.371%   $71.0043   $71.00   $71.00   $71.00  
  Purchase #2 $135.79   10.749%   $150.3861   $150.39   $150.40   $150.40  
  Purchase #3 $139.40   11.647%   $155.6359   $155.64   $155.65   $155.60  
  Purchase #4 $37.56   13.120%   $42.4879   $42.49   $42.50   $42.50  
  Purchase #5 $182.75   5.788%   $193.3276   $193.33   $193.35   $193.30  
  Purchase #6 $195.69   3.857%   $203.2378   $203.24   $203.25   $203.20  
  Purchase #7 $189.70   7.203%   $203.3641   $203.36   $203.35   $203.40  
  7 purchase totals = $943.52       $1,019.4437   $1,019.45   $1,019.50   $1,019.40