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 $61.66   13.581%   $70.034   $70.03   $70.05   $70.00  
  Purchase #2 $82.44   7.612%   $88.7153   $88.72   $88.70   $88.70  
  Purchase #3 $236.83   4.345%   $247.1203   $247.12   $247.10   $247.10  
  Purchase #4 $6.76   6.517%   $7.2005   $7.20   $7.20   $7.20  
  Purchase #5 $94.63   6.766%   $101.0327   $101.03   $101.05   $101.00  
  Purchase #6 $151.40   8.599%   $164.4189   $164.42   $164.40   $164.40  
  Purchase #7 $20.67   8.784%   $22.4857   $22.49   $22.50   $22.50  
  7 purchase totals = $654.39       $701.0074   $701.01   $701.00   $700.90