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 $184.83   3.748%   $191.7574   $191.76   $191.75   $191.80  
  Purchase #2 $244.73   3.737%   $253.8756   $253.88   $253.90   $253.90  
  Purchase #3 $41.59   5.712%   $43.9656   $43.97   $43.95   $44.00  
  Purchase #4 $194.94   5.827%   $206.2992   $206.30   $206.30   $206.30  
  Purchase #5 $94.30   7.490%   $101.3631   $101.36   $101.35   $101.40  
  Purchase #6 $241.58   3.435%   $249.8783   $249.88   $249.90   $249.90  
  Purchase #7 $23.72   13.611%   $26.9485   $26.95   $26.95   $26.90  
  7 purchase totals = $1,025.69       $1,074.0877   $1,074.10   $1,074.10   $1,074.20