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 $69.74   11.447%   $77.7231   $77.72   $77.70   $77.70  
  Purchase #2 $222.79   10.152%   $245.4076   $245.41   $245.40   $245.40  
  Purchase #3 $199.72   8.307%   $216.3107   $216.31   $216.30   $216.30  
  Purchase #4 $242.28   8.801%   $263.6031   $263.60   $263.60   $263.60  
  Purchase #5 $148.83   11.423%   $165.8309   $165.83   $165.85   $165.80  
  Purchase #6 $246.77   7.661%   $265.675   $265.68   $265.70   $265.70  
  Purchase #7 $116.49   3.305%   $120.34   $120.34   $120.35   $120.30  
  7 purchase totals = $1,246.62       $1,354.8904   $1,354.89   $1,354.90   $1,354.80