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 $61.88   9.711%   $67.8892   $67.89   $67.90   $67.90  
  Purchase #2 $75.30   10.546%   $83.2411   $83.24   $83.25   $83.20  
  Purchase #3 $24.49   12.584%   $27.5718   $27.57   $27.55   $27.60  
  Purchase #4 $236.66   11.438%   $263.7292   $263.73   $263.75   $263.70  
  Purchase #5 $88.73   13.431%   $100.6473   $100.65   $100.65   $100.60  
  Purchase #6 $26.88   5.692%   $28.41   $28.41   $28.40   $28.40  
  Purchase #7 $121.35   3.841%   $126.0111   $126.01   $126.00   $126.00  
  7 purchase totals = $635.29       $697.4997   $697.50   $697.50   $697.40