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 $53.84   13.451%   $61.082   $61.08   $61.10   $61.10  
  Purchase #2 $201.31   5.131%   $211.6392   $211.64   $211.65   $211.60  
  Purchase #3 $50.76   8.514%   $55.0817   $55.08   $55.10   $55.10  
  Purchase #4 $227.95   8.739%   $247.8706   $247.87   $247.85   $247.90  
  Purchase #5 $250.78   13.404%   $284.3946   $284.39   $284.40   $284.40  
  Purchase #6 $153.34   4.834%   $160.7525   $160.75   $160.75   $160.80  
  Purchase #7 $231.46   9.703%   $253.9186   $253.92   $253.90   $253.90  
  7 purchase totals = $1,169.44       $1,274.7392   $1,274.73   $1,274.75   $1,274.80