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 $68.28   3.374%   $70.5838   $70.58   $70.60   $70.60  
  Purchase #2 $168.46   13.385%   $191.0084   $191.01   $191.00   $191.00  
  Purchase #3 $243.83   8.661%   $264.9481   $264.95   $264.95   $264.90  
  Purchase #4 $131.76   12.568%   $148.3196   $148.32   $148.30   $148.30  
  Purchase #5 $217.26   3.780%   $225.4724   $225.47   $225.45   $225.50  
  Purchase #6 $142.47   13.556%   $161.7832   $161.78   $161.80   $161.80  
  Purchase #7 $9.31   9.106%   $10.1578   $10.16   $10.15   $10.20  
  7 purchase totals = $981.37       $1,072.2733   $1,072.27   $1,072.25   $1,072.30