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 $21.67   4.353%   $22.6133   $22.61   $22.60   $22.60  
  Purchase #2 $11.80   8.624%   $12.8176   $12.82   $12.80   $12.80  
  Purchase #3 $110.92   10.727%   $122.8184   $122.82   $122.80   $122.80  
  Purchase #4 $217.28   13.276%   $246.1261   $246.13   $246.15   $246.10  
  Purchase #5 $56.73   12.801%   $63.992   $63.99   $64.00   $64.00  
  Purchase #6 $229.76   12.497%   $258.4731   $258.47   $258.45   $258.50  
  Purchase #7 $85.91   4.320%   $89.6213   $89.62   $89.60   $89.60  
  7 purchase totals = $734.07       $816.4618   $816.46   $816.40   $816.40