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 $68.66   3.386%   $70.9848   $70.98   $71.00   $71.00  
  Purchase #2 $228.89   6.150%   $242.9667   $242.97   $242.95   $243.00  
  Purchase #3 $128.29   4.721%   $134.3466   $134.35   $134.35   $134.30  
  Purchase #4 $209.69   8.304%   $227.1027   $227.10   $227.10   $227.10  
  Purchase #5 $222.87   11.259%   $247.9629   $247.96   $247.95   $248.00  
  Purchase #6 $161.33   7.382%   $173.2394   $173.24   $173.25   $173.20  
  Purchase #7 $225.96   4.370%   $235.8345   $235.83   $235.85   $235.80  
  7 purchase totals = $1,245.69       $1,332.4376   $1,332.43   $1,332.45   $1,332.40