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 $168.40   8.611%   $182.9009   $182.90   $182.90   $182.90  
  Purchase #2 $173.77   13.445%   $197.1334   $197.13   $197.15   $197.10  
  Purchase #3 $190.36   12.363%   $213.8942   $213.89   $213.90   $213.90  
  Purchase #4 $98.65   10.309%   $108.8198   $108.82   $108.80   $108.80  
  Purchase #5 $160.64   4.868%   $168.46   $168.46   $168.45   $168.50  
  Purchase #6 $14.32   8.631%   $15.556   $15.56   $15.55   $15.60  
  Purchase #7 $144.51   5.185%   $152.0028   $152.00   $152.00   $152.00  
  7 purchase totals = $950.65       $1,038.7671   $1,038.76   $1,038.75   $1,038.80