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 $219.35   6.211%   $232.9738   $232.97   $232.95   $233.00  
  Purchase #2 $93.51   4.492%   $97.7105   $97.71   $97.70   $97.70  
  Purchase #3 $227.61   7.614%   $244.9402   $244.94   $244.95   $244.90  
  Purchase #4 $52.97   12.448%   $59.5637   $59.56   $59.55   $59.60  
  Purchase #5 $39.63   5.361%   $41.7546   $41.75   $41.75   $41.80  
  Purchase #6 $175.54   3.846%   $182.2913   $182.29   $182.30   $182.30  
  Purchase #7 $187.51   12.656%   $211.2413   $211.24   $211.25   $211.20  
  7 purchase totals = $996.12       $1,070.4754   $1,070.46   $1,070.45   $1,070.50