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 $69.71   5.666%   $73.6598   $73.66   $73.65   $73.70  
  Purchase #2 $125.80   9.652%   $137.9422   $137.94   $137.95   $137.90  
  Purchase #3 $89.42   5.650%   $94.4722   $94.47   $94.45   $94.50  
  Purchase #4 $228.77   4.147%   $238.2571   $238.26   $238.25   $238.30  
  Purchase #5 $130.59   4.781%   $136.8335   $136.83   $136.85   $136.80  
  Purchase #6 $66.54   5.128%   $69.9522   $69.95   $69.95   $70.00  
  Purchase #7 $38.76   7.341%   $41.6054   $41.61   $41.60   $41.60  
  7 purchase totals = $749.59       $792.7224   $792.72   $792.70   $792.80