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 $204.85   4.410%   $213.8839   $213.88   $213.90   $213.90  
  Purchase #2 $191.63   8.399%   $207.725   $207.73   $207.75   $207.70  
  Purchase #3 $13.45   11.623%   $15.0133   $15.01   $15.00   $15.00  
  Purchase #4 $145.32   7.334%   $155.9778   $155.98   $156.00   $156.00  
  Purchase #5 $38.98   7.311%   $41.8298   $41.83   $41.85   $41.80  
  Purchase #6 $105.43   13.675%   $119.8476   $119.85   $119.85   $119.80  
  Purchase #7 $229.32   5.529%   $241.9991   $242.00   $242.00   $242.00  
  7 purchase totals = $928.98       $996.2765   $996.28   $996.35   $996.20