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 $56.81   7.648%   $61.1548   $61.15   $61.15   $61.20  
  Purchase #2 $243.42   13.691%   $276.7466   $276.75   $276.75   $276.70  
  Purchase #3 $55.29   5.204%   $58.1673   $58.17   $58.15   $58.20  
  Purchase #4 $239.47   3.116%   $246.9319   $246.93   $246.95   $246.90  
  Purchase #5 $171.84   5.159%   $180.7052   $180.71   $180.70   $180.70  
  Purchase #6 $42.96   5.206%   $45.1965   $45.20   $45.20   $45.20  
  Purchase #7 $55.76   9.123%   $60.847   $60.85   $60.85   $60.80  
  7 purchase totals = $865.55       $929.7493   $929.76   $929.75   $929.70