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 $216.85   12.185%   $243.2732   $243.27   $243.25   $243.30  
  Purchase #2 $147.76   4.109%   $153.8315   $153.83   $153.85   $153.80  
  Purchase #3 $111.54   13.636%   $126.7496   $126.75   $126.75   $126.70  
  Purchase #4 $67.36   11.631%   $75.1946   $75.19   $75.20   $75.20  
  Purchase #5 $216.71   3.204%   $223.6534   $223.65   $223.65   $223.70  
  Purchase #6 $93.79   8.413%   $101.6806   $101.68   $101.70   $101.70  
  Purchase #7 $157.32   11.432%   $175.3048   $175.30   $175.30   $175.30  
  7 purchase totals = $1,011.33       $1,099.6877   $1,099.67   $1,099.70   $1,099.70