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 $150.85   11.247%   $167.8161   $167.82   $167.80   $167.80  
  Purchase #2 $72.56   9.660%   $79.5693   $79.57   $79.55   $79.60  
  Purchase #3 $184.98   7.776%   $199.364   $199.36   $199.35   $199.40  
  Purchase #4 $121.86   4.420%   $127.2462   $127.25   $127.25   $127.20  
  Purchase #5 $245.28   11.163%   $272.6606   $272.66   $272.65   $272.70  
  Purchase #6 $40.25   3.698%   $41.7384   $41.74   $41.75   $41.70  
  Purchase #7 $108.87   8.109%   $117.6983   $117.70   $117.70   $117.70  
  7 purchase totals = $924.65       $1,006.0929   $1,006.10   $1,006.05   $1,006.10