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 $108.40   4.789%   $113.5913   $113.59   $113.60   $113.60  
  Purchase #2 $77.49   9.349%   $84.7345   $84.73   $84.75   $84.70  
  Purchase #3 $26.25   7.337%   $28.176   $28.18   $28.20   $28.20  
  Purchase #4 $152.85   3.510%   $158.215   $158.22   $158.20   $158.20  
  Purchase #5 $203.44   7.175%   $218.0368   $218.04   $218.05   $218.00  
  Purchase #6 $167.78   12.392%   $188.5713   $188.57   $188.55   $188.60  
  Purchase #7 $218.85   11.686%   $244.4248   $244.42   $244.40   $244.40  
  7 purchase totals = $955.06       $1,035.7497   $1,035.75   $1,035.75   $1,035.70