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 $231.50   12.760%   $261.0394   $261.04   $261.05   $261.00  
  Purchase #2 $41.66   10.454%   $46.0151   $46.02   $46.00   $46.00  
  Purchase #3 $177.32   13.437%   $201.1465   $201.15   $201.15   $201.10  
  Purchase #4 $132.80   3.390%   $137.3019   $137.30   $137.30   $137.30  
  Purchase #5 $184.65   5.500%   $194.8058   $194.81   $194.80   $194.80  
  Purchase #6 $96.89   10.296%   $106.8658   $106.87   $106.85   $106.90  
  Purchase #7 $49.35   4.419%   $51.5308   $51.53   $51.55   $51.50  
  7 purchase totals = $914.17       $998.7053   $998.72   $998.70   $998.60