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 $61.39   9.486%   $67.2135   $67.21   $67.20   $67.20  
  Purchase #2 $98.26   12.786%   $110.8235   $110.82   $110.80   $110.80  
  Purchase #3 $17.35   7.627%   $18.6733   $18.67   $18.65   $18.70  
  Purchase #4 $239.49   10.861%   $265.501   $265.50   $265.50   $265.50  
  Purchase #5 $11.90   12.372%   $13.3723   $13.37   $13.35   $13.40  
  Purchase #6 $65.79   12.555%   $74.0499   $74.05   $74.05   $74.00  
  Purchase #7 $201.94   11.423%   $225.0076   $225.01   $225.00   $225.00  
  7 purchase totals = $696.12       $774.6411   $774.63   $774.55   $774.60