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 $46.48   5.123%   $48.8612   $48.86   $48.85   $48.90  
  Purchase #2 $181.45   6.846%   $193.8721   $193.87   $193.85   $193.90  
  Purchase #3 $246.59   7.852%   $265.9522   $265.95   $265.95   $266.00  
  Purchase #4 $157.26   10.797%   $174.2394   $174.24   $174.25   $174.20  
  Purchase #5 $8.80   11.689%   $9.8286   $9.83   $9.85   $9.80  
  Purchase #6 $37.26   9.868%   $40.9368   $40.94   $40.95   $40.90  
  Purchase #7 $28.96   4.601%   $30.2924   $30.29   $30.30   $30.30  
  7 purchase totals = $706.80       $763.9827   $763.98   $764.00   $764.00