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 $145.36   7.178%   $155.7939   $155.79   $155.80   $155.80  
  Purchase #2 $141.38   9.728%   $155.1334   $155.13   $155.15   $155.10  
  Purchase #3 $99.74   8.377%   $108.0952   $108.10   $108.10   $108.10  
  Purchase #4 $155.64   4.863%   $163.2088   $163.21   $163.20   $163.20  
  Purchase #5 $72.90   3.639%   $75.5528   $75.55   $75.55   $75.60  
  Purchase #6 $9.87   6.758%   $10.537   $10.54   $10.55   $10.50  
  Purchase #7 $66.49   6.817%   $71.0226   $71.02   $71.00   $71.00  
  7 purchase totals = $691.38       $739.3437   $739.34   $739.35   $739.30