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 $30.26   8.783%   $32.9177   $32.92   $32.90   $32.90  
  Purchase #2 $233.94   9.134%   $255.3081   $255.31   $255.30   $255.30  
  Purchase #3 $81.36   8.514%   $88.287   $88.29   $88.30   $88.30  
  Purchase #4 $117.68   11.613%   $131.3462   $131.35   $131.35   $131.30  
  Purchase #5 $246.77   6.577%   $263.0001   $263.00   $263.00   $263.00  
  Purchase #6 $247.87   4.550%   $259.1481   $259.15   $259.15   $259.10  
  Purchase #7 $85.46   7.650%   $91.9977   $92.00   $92.00   $92.00  
  7 purchase totals = $1,043.34       $1,122.0049   $1,122.02   $1,122.00   $1,121.90