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 $203.66   3.151%   $210.0773   $210.08   $210.10   $210.10  
  Purchase #2 $122.85   3.247%   $126.8389   $126.84   $126.85   $126.80  
  Purchase #3 $211.37   13.138%   $239.1398   $239.14   $239.15   $239.10  
  Purchase #4 $194.81   5.163%   $204.868   $204.87   $204.85   $204.90  
  Purchase #5 $228.82   3.147%   $236.021   $236.02   $236.00   $236.00  
  Purchase #6 $123.41   3.510%   $127.7417   $127.74   $127.75   $127.70  
  Purchase #7 $191.83   5.681%   $202.7279   $202.73   $202.75   $202.70  
  7 purchase totals = $1,276.75       $1,347.4146   $1,347.42   $1,347.45   $1,347.30