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 $61.82   3.819%   $64.1809   $64.18   $64.20   $64.20  
  Purchase #2 $58.31   11.632%   $65.0926   $65.09   $65.10   $65.10  
  Purchase #3 $98.81   6.849%   $105.5775   $105.58   $105.60   $105.60  
  Purchase #4 $195.62   11.602%   $218.3158   $218.32   $218.30   $218.30  
  Purchase #5 $131.74   4.333%   $137.4483   $137.45   $137.45   $137.40  
  Purchase #6 $126.91   9.264%   $138.6669   $138.67   $138.65   $138.70  
  Purchase #7 $210.64   11.128%   $234.08   $234.08   $234.10   $234.10  
  7 purchase totals = $883.85       $963.3620   $963.37   $963.40   $963.40