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 $104.58   11.827%   $116.9487   $116.95   $116.95   $116.90  
  Purchase #2 $218.98   12.181%   $245.654   $245.65   $245.65   $245.70  
  Purchase #3 $8.74   3.687%   $9.0622   $9.06   $9.05   $9.10  
  Purchase #4 $249.27   7.795%   $268.7006   $268.70   $268.70   $268.70  
  Purchase #5 $84.34   11.713%   $94.2187   $94.22   $94.20   $94.20  
  Purchase #6 $163.69   11.861%   $183.1053   $183.11   $183.10   $183.10  
  Purchase #7 $125.52   12.272%   $140.9238   $140.92   $140.90   $140.90  
  7 purchase totals = $955.12       $1,058.6133   $1,058.61   $1,058.55   $1,058.60