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 $245.59   5.744%   $259.6967   $259.70   $259.70   $259.70  
  Purchase #2 $177.86   6.412%   $189.2644   $189.26   $189.25   $189.30  
  Purchase #3 $27.27   6.605%   $29.0712   $29.07   $29.05   $29.10  
  Purchase #4 $8.69   6.596%   $9.2632   $9.26   $9.25   $9.30  
  Purchase #5 $118.80   4.845%   $124.5559   $124.56   $124.55   $124.60  
  Purchase #6 $151.37   4.144%   $157.6428   $157.64   $157.65   $157.60  
  Purchase #7 $37.52   11.431%   $41.8089   $41.81   $41.80   $41.80  
  7 purchase totals = $767.10       $811.3031   $811.30   $811.25   $811.40