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 $83.41   11.260%   $92.802   $92.80   $92.80   $92.80  
  Purchase #2 $210.99   7.269%   $226.3269   $226.33   $226.35   $226.30  
  Purchase #3 $234.42   3.111%   $241.7128   $241.71   $241.70   $241.70  
  Purchase #4 $237.88   9.633%   $260.795   $260.80   $260.80   $260.80  
  Purchase #5 $15.99   5.757%   $16.9105   $16.91   $16.90   $16.90  
  Purchase #6 $179.77   3.625%   $186.2867   $186.29   $186.30   $186.30  
  Purchase #7 $50.61   7.401%   $54.3556   $54.36   $54.35   $54.40  
  7 purchase totals = $1,013.07       $1,079.1895   $1,079.20   $1,079.20   $1,079.20