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 $23.95   9.819%   $26.3017   $26.30   $26.30   $26.30  
  Purchase #2 $86.94   6.284%   $92.4033   $92.40   $92.40   $92.40  
  Purchase #3 $101.27   10.574%   $111.9783   $111.98   $112.00   $112.00  
  Purchase #4 $213.41   10.230%   $235.2418   $235.24   $235.25   $235.20  
  Purchase #5 $78.93   4.171%   $82.2222   $82.22   $82.20   $82.20  
  Purchase #6 $121.68   7.783%   $131.1504   $131.15   $131.15   $131.20  
  Purchase #7 $65.25   9.690%   $71.5727   $71.57   $71.55   $71.60  
  7 purchase totals = $691.43       $750.8704   $750.86   $750.85   $750.90