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 $116.53   6.810%   $124.4657   $124.47   $124.45   $124.50  
  Purchase #2 $192.38   5.357%   $202.6858   $202.69   $202.70   $202.70  
  Purchase #3 $128.79   6.544%   $137.218   $137.22   $137.20   $137.20  
  Purchase #4 $69.88   9.286%   $76.3691   $76.37   $76.35   $76.40  
  Purchase #5 $40.85   11.770%   $45.658   $45.66   $45.65   $45.70  
  Purchase #6 $178.37   10.464%   $197.0346   $197.03   $197.05   $197.00  
  Purchase #7 $55.97   7.425%   $60.1258   $60.13   $60.15   $60.10  
  7 purchase totals = $782.77       $843.5570   $843.57   $843.55   $843.60