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 $57.48   3.682%   $59.5964   $59.60   $59.60   $59.60  
  Purchase #2 $164.85   6.564%   $175.6708   $175.67   $175.65   $175.70  
  Purchase #3 $62.99   12.647%   $70.9563   $70.96   $70.95   $71.00  
  Purchase #4 $94.71   11.704%   $105.7949   $105.79   $105.80   $105.80  
  Purchase #5 $210.77   12.299%   $236.6926   $236.69   $236.70   $236.70  
  Purchase #6 $72.31   11.860%   $80.886   $80.89   $80.90   $80.90  
  Purchase #7 $22.63   6.435%   $24.0862   $24.09   $24.10   $24.10  
  7 purchase totals = $685.74       $753.6832   $753.69   $753.70   $753.80