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 $104.95   7.762%   $113.0962   $113.10   $113.10   $113.10  
  Purchase #2 $16.90   8.517%   $18.3394   $18.34   $18.35   $18.30  
  Purchase #3 $222.69   7.144%   $238.599   $238.60   $238.60   $238.60  
  Purchase #4 $162.37   12.345%   $182.4146   $182.41   $182.40   $182.40  
  Purchase #5 $46.52   12.828%   $52.4876   $52.49   $52.50   $52.50  
  Purchase #6 $188.25   13.820%   $214.2662   $214.27   $214.25   $214.30  
  Purchase #7 $185.36   8.434%   $200.9933   $200.99   $201.00   $201.00  
  7 purchase totals = $927.04       $1,020.1963   $1,020.20   $1,020.20   $1,020.20