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 $22.57   12.112%   $25.3037   $25.30   $25.30   $25.30  
  Purchase #2 $162.25   8.624%   $176.2424   $176.24   $176.25   $176.20  
  Purchase #3 $154.42   3.518%   $159.8525   $159.85   $159.85   $159.90  
  Purchase #4 $71.74   8.628%   $77.9297   $77.93   $77.95   $77.90  
  Purchase #5 $41.86   8.175%   $45.2821   $45.28   $45.30   $45.30  
  Purchase #6 $37.85   8.106%   $40.9181   $40.92   $40.90   $40.90  
  Purchase #7 $223.32   6.312%   $237.416   $237.42   $237.40   $237.40  
  7 purchase totals = $714.01       $762.9445   $762.94   $762.95   $762.90