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 $88.27   9.632%   $96.7722   $96.77   $96.75   $96.80  
  Purchase #2 $132.93   5.789%   $140.6253   $140.63   $140.65   $140.60  
  Purchase #3 $234.85   5.174%   $247.0011   $247.00   $247.00   $247.00  
  Purchase #4 $214.31   10.176%   $236.1182   $236.12   $236.10   $236.10  
  Purchase #5 $131.74   12.444%   $148.1337   $148.13   $148.15   $148.10  
  Purchase #6 $222.49   10.605%   $246.0851   $246.09   $246.10   $246.10  
  Purchase #7 $123.80   9.300%   $135.3134   $135.31   $135.30   $135.30  
  7 purchase totals = $1,148.39       $1,250.0490   $1,250.05   $1,250.05   $1,250.00