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 $167.79   11.169%   $186.5305   $186.53   $186.55   $186.50  
  Purchase #2 $21.54   10.228%   $23.7431   $23.74   $23.75   $23.70  
  Purchase #3 $90.81   4.814%   $95.1816   $95.18   $95.20   $95.20  
  Purchase #4 $101.38   3.262%   $104.687   $104.69   $104.70   $104.70  
  Purchase #5 $168.35   8.431%   $182.5436   $182.54   $182.55   $182.50  
  Purchase #6 $184.44   10.443%   $203.7011   $203.70   $203.70   $203.70  
  Purchase #7 $120.88   8.716%   $131.4159   $131.42   $131.40   $131.40  
  7 purchase totals = $855.19       $927.8028   $927.80   $927.85   $927.70