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 $156.89   10.486%   $173.3415   $173.34   $173.35   $173.30  
  Purchase #2 $109.69   9.361%   $119.9581   $119.96   $119.95   $120.00  
  Purchase #3 $34.83   9.798%   $38.2426   $38.24   $38.25   $38.20  
  Purchase #4 $114.94   5.648%   $121.4318   $121.43   $121.45   $121.40  
  Purchase #5 $223.93   3.658%   $232.1214   $232.12   $232.10   $232.10  
  Purchase #6 $188.50   9.659%   $206.7072   $206.71   $206.70   $206.70  
  Purchase #7 $185.61   5.864%   $196.4942   $196.49   $196.50   $196.50  
  7 purchase totals = $1,014.39       $1,088.2968   $1,088.29   $1,088.30   $1,088.20