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 $219.35   10.311%   $241.9672   $241.97   $241.95   $242.00  
  Purchase #2 $136.51   12.448%   $153.5028   $153.50   $153.50   $153.50  
  Purchase #3 $21.28   12.363%   $23.9108   $23.91   $23.90   $23.90  
  Purchase #4 $50.84   11.203%   $56.5356   $56.54   $56.55   $56.50  
  Purchase #5 $216.76   3.234%   $223.77   $223.77   $223.75   $223.80  
  Purchase #6 $14.33   3.308%   $14.804   $14.80   $14.80   $14.80  
  Purchase #7 $233.47   7.566%   $251.1343   $251.13   $251.15   $251.10  
  7 purchase totals = $892.54       $965.6247   $965.62   $965.60   $965.60