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 $164.68   12.726%   $185.6372   $185.64   $185.65   $185.60  
  Purchase #2 $34.69   3.544%   $35.9194   $35.92   $35.90   $35.90  
  Purchase #3 $160.31   12.330%   $180.0762   $180.08   $180.10   $180.10  
  Purchase #4 $117.68   5.541%   $124.2006   $124.20   $124.20   $124.20  
  Purchase #5 $173.83   4.318%   $181.336   $181.34   $181.35   $181.30  
  Purchase #6 $150.51   5.853%   $159.3194   $159.32   $159.30   $159.30  
  Purchase #7 $161.27   5.857%   $170.7156   $170.72   $170.70   $170.70  
  7 purchase totals = $962.97       $1,037.2044   $1,037.22   $1,037.20   $1,037.10