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 $104.71   12.652%   $117.9579   $117.96   $117.95   $118.00  
  Purchase #2 $120.98   10.479%   $133.6575   $133.66   $133.65   $133.70  
  Purchase #3 $174.88   8.426%   $189.6154   $189.62   $189.60   $189.60  
  Purchase #4 $212.27   11.671%   $237.044   $237.04   $237.05   $237.00  
  Purchase #5 $115.86   7.729%   $124.8148   $124.81   $124.80   $124.80  
  Purchase #6 $183.85   10.730%   $203.5771   $203.58   $203.60   $203.60  
  Purchase #7 $250.68   6.343%   $266.5806   $266.58   $266.60   $266.60  
  7 purchase totals = $1,163.23       $1,273.2473   $1,273.25   $1,273.25   $1,273.30