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 $116.56   13.213%   $131.9611   $131.96   $131.95   $132.00  
  Purchase #2 $124.60   4.571%   $130.2955   $130.30   $130.30   $130.30  
  Purchase #3 $232.76   3.430%   $240.7437   $240.74   $240.75   $240.70  
  Purchase #4 $126.76   5.254%   $133.42   $133.42   $133.40   $133.40  
  Purchase #5 $201.61   12.119%   $226.0431   $226.04   $226.05   $226.00  
  Purchase #6 $24.29   12.380%   $27.2971   $27.30   $27.30   $27.30  
  Purchase #7 $225.36   4.851%   $236.2922   $236.29   $236.30   $236.30  
  7 purchase totals = $1,051.94       $1,126.0527   $1,126.05   $1,126.05   $1,126.00