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 $216.49   12.481%   $243.5101   $243.51   $243.50   $243.50  
  Purchase #2 $114.62   4.560%   $119.8467   $119.85   $119.85   $119.80  
  Purchase #3 $46.37   11.861%   $51.8699   $51.87   $51.85   $51.90  
  Purchase #4 $135.25   13.401%   $153.3749   $153.37   $153.35   $153.40  
  Purchase #5 $83.35   12.376%   $93.6654   $93.67   $93.65   $93.70  
  Purchase #6 $24.82   12.147%   $27.8349   $27.83   $27.85   $27.80  
  Purchase #7 $56.73   11.125%   $63.0412   $63.04   $63.05   $63.00  
  7 purchase totals = $677.63       $753.1431   $753.14   $753.10   $753.10