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 $180.65   11.597%   $201.6   $201.60   $201.60   $201.60  
  Purchase #2 $15.94   7.285%   $17.1012   $17.10   $17.10   $17.10  
  Purchase #3 $226.95   12.282%   $254.824   $254.82   $254.80   $254.80  
  Purchase #4 $23.66   5.232%   $24.8979   $24.90   $24.90   $24.90  
  Purchase #5 $94.64   7.520%   $101.7569   $101.76   $101.75   $101.80  
  Purchase #6 $79.74   3.184%   $82.2789   $82.28   $82.30   $82.30  
  Purchase #7 $191.68   9.593%   $210.0679   $210.07   $210.05   $210.10  
  7 purchase totals = $813.26       $892.5268   $892.53   $892.50   $892.60