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 $91.61   11.201%   $101.8712   $101.87   $101.85   $101.90  
  Purchase #2 $23.61   6.731%   $25.1992   $25.20   $25.20   $25.20  
  Purchase #3 $246.66   12.318%   $277.0436   $277.04   $277.05   $277.00  
  Purchase #4 $245.44   4.266%   $255.9105   $255.91   $255.90   $255.90  
  Purchase #5 $78.93   7.778%   $85.0692   $85.07   $85.05   $85.10  
  Purchase #6 $81.94   13.121%   $92.6913   $92.69   $92.70   $92.70  
  Purchase #7 $106.35   4.670%   $111.3165   $111.32   $111.30   $111.30  
  7 purchase totals = $874.54       $949.1015   $949.10   $949.05   $949.10