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 $61.78   3.490%   $63.9361   $63.94   $63.95   $63.90  
  Purchase #2 $154.60   13.819%   $175.9642   $175.96   $175.95   $176.00  
  Purchase #3 $10.93   10.438%   $12.0709   $12.07   $12.05   $12.10  
  Purchase #4 $31.41   11.447%   $35.0055   $35.01   $35.00   $35.00  
  Purchase #5 $239.59   3.644%   $248.3207   $248.32   $248.30   $248.30  
  Purchase #6 $74.92   9.477%   $82.0202   $82.02   $82.00   $82.00  
  Purchase #7 $145.47   3.103%   $149.9839   $149.98   $150.00   $150.00  
  7 purchase totals = $718.70       $767.3015   $767.30   $767.25   $767.30