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 $174.89   5.166%   $183.9248   $183.92   $183.90   $183.90  
  Purchase #2 $33.57   13.857%   $38.2218   $38.22   $38.20   $38.20  
  Purchase #3 $219.57   5.580%   $231.822   $231.82   $231.80   $231.80  
  Purchase #4 $38.96   5.858%   $41.2423   $41.24   $41.25   $41.20  
  Purchase #5 $61.89   5.125%   $65.0619   $65.06   $65.05   $65.10  
  Purchase #6 $151.61   7.581%   $163.1036   $163.10   $163.10   $163.10  
  Purchase #7 $186.87   13.220%   $211.5742   $211.57   $211.55   $211.60  
  7 purchase totals = $867.36       $934.9506   $934.93   $934.85   $934.90