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 $62.47   3.539%   $64.6808   $64.68   $64.70   $64.70  
  Purchase #2 $241.46   11.527%   $269.2931   $269.29   $269.30   $269.30  
  Purchase #3 $220.90   10.532%   $244.1652   $244.17   $244.15   $244.20  
  Purchase #4 $21.34   4.639%   $22.33   $22.33   $22.35   $22.30  
  Purchase #5 $70.70   8.482%   $76.6968   $76.70   $76.70   $76.70  
  Purchase #6 $110.98   6.832%   $118.5622   $118.56   $118.55   $118.60  
  Purchase #7 $27.67   11.596%   $30.8786   $30.88   $30.90   $30.90  
  7 purchase totals = $755.52       $826.6067   $826.61   $826.65   $826.70