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 $246.76   4.575%   $258.0493   $258.05   $258.05   $258.00  
  Purchase #2 $208.43   5.580%   $220.0604   $220.06   $220.05   $220.10  
  Purchase #3 $88.74   7.629%   $95.51   $95.51   $95.50   $95.50  
  Purchase #4 $22.43   7.620%   $24.1392   $24.14   $24.15   $24.10  
  Purchase #5 $115.26   3.488%   $119.2803   $119.28   $119.30   $119.30  
  Purchase #6 $178.32   12.631%   $200.8436   $200.84   $200.85   $200.80  
  Purchase #7 $23.89   11.107%   $26.5435   $26.54   $26.55   $26.50  
  7 purchase totals = $883.83       $944.4263   $944.42   $944.45   $944.30