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 $194.87   3.205%   $201.1156   $201.12   $201.10   $201.10  
  Purchase #2 $33.94   3.143%   $35.0067   $35.01   $35.00   $35.00  
  Purchase #3 $6.88   11.439%   $7.667   $7.67   $7.65   $7.70  
  Purchase #4 $91.40   13.710%   $103.9309   $103.93   $103.95   $103.90  
  Purchase #5 $193.71   10.712%   $214.4602   $214.46   $214.45   $214.50  
  Purchase #6 $70.35   3.669%   $72.9311   $72.93   $72.95   $72.90  
  Purchase #7 $66.98   6.301%   $71.2004   $71.20   $71.20   $71.20  
  7 purchase totals = $658.13       $706.3119   $706.32   $706.30   $706.30