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 $60.75   4.783%   $63.6557   $63.66   $63.65   $63.70  
  Purchase #2 $76.47   5.327%   $80.5436   $80.54   $80.55   $80.50  
  Purchase #3 $186.46   4.414%   $194.6903   $194.69   $194.70   $194.70  
  Purchase #4 $99.74   8.249%   $107.9676   $107.97   $107.95   $108.00  
  Purchase #5 $209.96   5.616%   $221.7514   $221.75   $221.75   $221.80  
  Purchase #6 $128.94   6.135%   $136.8505   $136.85   $136.85   $136.90  
  Purchase #7 $231.75   5.416%   $244.3016   $244.30   $244.30   $244.30  
  7 purchase totals = $994.07       $1,049.7607   $1,049.76   $1,049.75   $1,049.90