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 $183.38   10.186%   $202.0591   $202.06   $202.05   $202.10  
  Purchase #2 $185.47   3.495%   $191.9522   $191.95   $191.95   $192.00  
  Purchase #3 $221.32   13.729%   $251.705   $251.71   $251.70   $251.70  
  Purchase #4 $56.41   13.562%   $64.0603   $64.06   $64.05   $64.10  
  Purchase #5 $204.43   13.189%   $231.3923   $231.39   $231.40   $231.40  
  Purchase #6 $10.59   10.694%   $11.7225   $11.72   $11.70   $11.70  
  Purchase #7 $93.84   4.635%   $98.1895   $98.19   $98.20   $98.20  
  7 purchase totals = $955.44       $1,051.0809   $1,051.08   $1,051.05   $1,051.20