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 $215.43   7.298%   $231.1521   $231.15   $231.15   $231.20  
  Purchase #2 $58.90   4.153%   $61.3461   $61.35   $61.35   $61.30  
  Purchase #3 $16.70   8.389%   $18.101   $18.10   $18.10   $18.10  
  Purchase #4 $153.90   5.584%   $162.4938   $162.49   $162.50   $162.50  
  Purchase #5 $128.98   3.270%   $133.1976   $133.20   $133.20   $133.20  
  Purchase #6 $22.44   4.510%   $23.452   $23.45   $23.45   $23.50  
  Purchase #7 $54.43   13.842%   $61.9642   $61.96   $61.95   $62.00  
  7 purchase totals = $650.78       $691.7068   $691.70   $691.70   $691.80