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 $62.73   12.129%   $70.3385   $70.34   $70.35   $70.30  
  Purchase #2 $186.29   5.279%   $196.1242   $196.12   $196.10   $196.10  
  Purchase #3 $161.47   8.546%   $175.2692   $175.27   $175.25   $175.30  
  Purchase #4 $250.62   4.289%   $261.3691   $261.37   $261.35   $261.40  
  Purchase #5 $109.42   6.424%   $116.4491   $116.45   $116.45   $116.40  
  Purchase #6 $177.92   5.310%   $187.3676   $187.37   $187.35   $187.40  
  Purchase #7 $70.28   3.867%   $72.9977   $73.00   $73.00   $73.00  
  7 purchase totals = $1,018.73       $1,079.9154   $1,079.92   $1,079.85   $1,079.90