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 $61.43   10.302%   $67.7585   $67.76   $67.75   $67.80  
  Purchase #2 $157.49   6.466%   $167.6733   $167.67   $167.65   $167.70  
  Purchase #3 $240.99   11.848%   $269.5425   $269.54   $269.55   $269.50  
  Purchase #4 $24.90   5.402%   $26.2451   $26.25   $26.25   $26.20  
  Purchase #5 $54.48   12.609%   $61.3494   $61.35   $61.35   $61.30  
  Purchase #6 $207.25   5.612%   $218.8809   $218.88   $218.90   $218.90  
  Purchase #7 $60.31   9.193%   $65.8543   $65.85   $65.85   $65.90  
  7 purchase totals = $806.85       $877.3040   $877.30   $877.30   $877.30