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 $109.28   7.123%   $117.064   $117.06   $117.05   $117.10  
  Purchase #2 $91.70   6.828%   $97.9613   $97.96   $97.95   $98.00  
  Purchase #3 $24.80   5.822%   $26.2439   $26.24   $26.25   $26.20  
  Purchase #4 $137.38   8.163%   $148.5943   $148.59   $148.60   $148.60  
  Purchase #5 $124.33   8.821%   $135.2971   $135.30   $135.30   $135.30  
  Purchase #6 $170.57   10.460%   $188.4116   $188.41   $188.40   $188.40  
  Purchase #7 $245.98   5.432%   $259.3416   $259.34   $259.35   $259.30  
  7 purchase totals = $904.04       $972.9138   $972.90   $972.90   $972.90