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 $228.60   12.704%   $257.6413   $257.64   $257.65   $257.60  
  Purchase #2 $154.87   8.189%   $167.5523   $167.55   $167.55   $167.60  
  Purchase #3 $151.39   13.687%   $172.1107   $172.11   $172.10   $172.10  
  Purchase #4 $61.69   5.428%   $65.0385   $65.04   $65.05   $65.00  
  Purchase #5 $157.35   4.797%   $164.8981   $164.90   $164.90   $164.90  
  Purchase #6 $229.67   7.130%   $246.0455   $246.05   $246.05   $246.00  
  Purchase #7 $45.76   12.873%   $51.6507   $51.65   $51.65   $51.70  
  7 purchase totals = $1,029.33       $1,124.9371   $1,124.94   $1,124.95   $1,124.90