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 $67.79   3.226%   $69.9769   $69.98   $70.00   $70.00  
  Purchase #2 $213.64   6.641%   $227.8278   $227.83   $227.85   $227.80  
  Purchase #3 $19.90   9.686%   $21.8275   $21.83   $21.85   $21.80  
  Purchase #4 $106.97   13.267%   $121.1617   $121.16   $121.15   $121.20  
  Purchase #5 $81.36   4.742%   $85.2181   $85.22   $85.20   $85.20  
  Purchase #6 $219.94   10.721%   $243.5198   $243.52   $243.50   $243.50  
  Purchase #7 $121.64   4.723%   $127.3851   $127.39   $127.40   $127.40  
  7 purchase totals = $831.24       $896.9169   $896.93   $896.95   $896.90