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 $85.70   13.689%   $97.4315   $97.43   $97.45   $97.40  
  Purchase #2 $173.59   12.315%   $194.9676   $194.97   $194.95   $195.00  
  Purchase #3 $27.49   8.595%   $29.8528   $29.85   $29.85   $29.90  
  Purchase #4 $84.94   13.633%   $96.5199   $96.52   $96.50   $96.50  
  Purchase #5 $57.51   10.291%   $63.4284   $63.43   $63.45   $63.40  
  Purchase #6 $104.64   13.584%   $118.8543   $118.85   $118.85   $118.90  
  Purchase #7 $173.90   12.445%   $195.5419   $195.54   $195.55   $195.50  
  7 purchase totals = $707.77       $796.5964   $796.59   $796.60   $796.60