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 $201.81   11.244%   $224.5015   $224.50   $224.50   $224.50  
  Purchase #2 $184.95   12.629%   $208.3073   $208.31   $208.30   $208.30  
  Purchase #3 $36.31   3.834%   $37.7021   $37.70   $37.70   $37.70  
  Purchase #4 $157.52   13.529%   $178.8309   $178.83   $178.85   $178.80  
  Purchase #5 $124.48   4.248%   $129.7679   $129.77   $129.75   $129.80  
  Purchase #6 $173.74   9.663%   $190.5285   $190.53   $190.55   $190.50  
  Purchase #7 $83.75   12.207%   $93.9734   $93.97   $93.95   $94.00  
  7 purchase totals = $962.56       $1,063.6116   $1,063.61   $1,063.60   $1,063.60