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 $22.92   6.635%   $24.4407   $24.44   $24.45   $24.40  
  Purchase #2 $134.72   9.596%   $147.6477   $147.65   $147.65   $147.60  
  Purchase #3 $157.33   9.217%   $171.8311   $171.83   $171.85   $171.80  
  Purchase #4 $7.92   9.376%   $8.6626   $8.66   $8.65   $8.70  
  Purchase #5 $247.59   12.378%   $278.2367   $278.24   $278.25   $278.20  
  Purchase #6 $160.86   3.376%   $166.2906   $166.29   $166.30   $166.30  
  Purchase #7 $200.59   9.422%   $219.4896   $219.49   $219.50   $219.50  
  7 purchase totals = $931.93       $1,016.5990   $1,016.60   $1,016.65   $1,016.50