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 $247.94   5.771%   $262.2486   $262.25   $262.25   $262.20  
  Purchase #2 $133.58   6.747%   $142.5926   $142.59   $142.60   $142.60  
  Purchase #3 $45.35   9.116%   $49.4841   $49.48   $49.50   $49.50  
  Purchase #4 $129.26   4.274%   $134.7846   $134.78   $134.80   $134.80  
  Purchase #5 $28.87   5.555%   $30.4737   $30.47   $30.45   $30.50  
  Purchase #6 $170.65   3.285%   $176.2559   $176.26   $176.25   $176.30  
  Purchase #7 $122.59   7.107%   $131.3025   $131.30   $131.30   $131.30  
  7 purchase totals = $878.24       $927.1420   $927.13   $927.15   $927.20