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 $188.65   12.747%   $212.6972   $212.70   $212.70   $212.70  
  Purchase #2 $149.88   11.106%   $166.5257   $166.53   $166.55   $166.50  
  Purchase #3 $67.54   6.129%   $71.6795   $71.68   $71.70   $71.70  
  Purchase #4 $70.97   4.135%   $73.9046   $73.90   $73.90   $73.90  
  Purchase #5 $144.36   7.158%   $154.6933   $154.69   $154.70   $154.70  
  Purchase #6 $102.84   7.571%   $110.626   $110.63   $110.65   $110.60  
  Purchase #7 $224.74   11.788%   $251.2324   $251.23   $251.25   $251.20  
  7 purchase totals = $948.98       $1,041.3587   $1,041.36   $1,041.45   $1,041.30