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 $28.55   12.121%   $32.0105   $32.01   $32.00   $32.00  
  Purchase #2 $207.99   4.283%   $216.8982   $216.90   $216.90   $216.90  
  Purchase #3 $193.74   5.323%   $204.0528   $204.05   $204.05   $204.10  
  Purchase #4 $141.77   6.305%   $150.7086   $150.71   $150.70   $150.70  
  Purchase #5 $224.80   9.849%   $246.9406   $246.94   $246.95   $246.90  
  Purchase #6 $109.78   4.299%   $114.4994   $114.50   $114.50   $114.50  
  Purchase #7 $90.46   8.312%   $97.979   $97.98   $98.00   $98.00  
  7 purchase totals = $997.09       $1,063.0891   $1,063.09   $1,063.10   $1,063.10