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 $88.38   6.283%   $93.9329   $93.93   $93.95   $93.90  
  Purchase #2 $235.57   9.789%   $258.6299   $258.63   $258.65   $258.60  
  Purchase #3 $127.92   5.239%   $134.6217   $134.62   $134.60   $134.60  
  Purchase #4 $167.80   11.842%   $187.6709   $187.67   $187.65   $187.70  
  Purchase #5 $61.44   3.380%   $63.5167   $63.52   $63.50   $63.50  
  Purchase #6 $43.62   5.595%   $46.0605   $46.06   $46.05   $46.10  
  Purchase #7 $169.76   5.232%   $178.6418   $178.64   $178.65   $178.60  
  7 purchase totals = $894.49       $963.0744   $963.07   $963.05   $963.00