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 $60.90   10.841%   $67.5022   $67.50   $67.50   $67.50  
  Purchase #2 $240.49   13.628%   $273.264   $273.26   $273.25   $273.30  
  Purchase #3 $155.48   5.766%   $164.445   $164.45   $164.45   $164.40  
  Purchase #4 $69.50   3.633%   $72.0249   $72.02   $72.00   $72.00  
  Purchase #5 $80.41   9.527%   $88.0707   $88.07   $88.05   $88.10  
  Purchase #6 $126.32   6.299%   $134.2769   $134.28   $134.30   $134.30  
  Purchase #7 $5.98   4.847%   $6.2699   $6.27   $6.25   $6.30  
  7 purchase totals = $739.08       $805.8536   $805.85   $805.80   $805.90