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 $236.95   12.230%   $265.929   $265.93   $265.95   $265.90  
  Purchase #2 $168.68   11.837%   $188.6467   $188.65   $188.65   $188.60  
  Purchase #3 $97.88   9.858%   $107.529   $107.53   $107.55   $107.50  
  Purchase #4 $67.72   5.439%   $71.4033   $71.40   $71.40   $71.40  
  Purchase #5 $169.93   9.265%   $185.674   $185.67   $185.65   $185.70  
  Purchase #6 $162.51   10.197%   $179.0811   $179.08   $179.10   $179.10  
  Purchase #7 $223.69   5.173%   $235.2615   $235.26   $235.25   $235.30  
  7 purchase totals = $1,127.36       $1,233.5246   $1,233.52   $1,233.55   $1,233.50