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 $137.31   9.444%   $150.2776   $150.28   $150.30   $150.30  
  Purchase #2 $190.89   12.466%   $214.6863   $214.69   $214.70   $214.70  
  Purchase #3 $38.73   10.307%   $42.7219   $42.72   $42.70   $42.70  
  Purchase #4 $211.44   3.530%   $218.9038   $218.90   $218.90   $218.90  
  Purchase #5 $68.70   9.135%   $74.9757   $74.98   $75.00   $75.00  
  Purchase #6 $27.88   8.299%   $30.1938   $30.19   $30.20   $30.20  
  Purchase #7 $205.94   8.669%   $223.7929   $223.79   $223.80   $223.80  
  7 purchase totals = $880.89       $955.5520   $955.55   $955.60   $955.60