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 $58.44   10.690%   $64.6872   $64.69   $64.70   $64.70  
  Purchase #2 $202.64   3.567%   $209.8682   $209.87   $209.85   $209.90  
  Purchase #3 $153.86   7.259%   $165.0287   $165.03   $165.05   $165.00  
  Purchase #4 $181.78   7.393%   $195.219   $195.22   $195.20   $195.20  
  Purchase #5 $109.72   6.291%   $116.6225   $116.62   $116.60   $116.60  
  Purchase #6 $35.99   5.325%   $37.9065   $37.91   $37.90   $37.90  
  Purchase #7 $204.45   7.196%   $219.1622   $219.16   $219.15   $219.20  
  7 purchase totals = $946.88       $1,008.4943   $1,008.50   $1,008.45   $1,008.50