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 $62.46   10.792%   $69.2007   $69.20   $69.20   $69.20  
  Purchase #2 $215.83   11.160%   $239.9166   $239.92   $239.90   $239.90  
  Purchase #3 $106.73   4.560%   $111.5969   $111.60   $111.60   $111.60  
  Purchase #4 $51.35   4.754%   $53.7912   $53.79   $53.80   $53.80  
  Purchase #5 $155.93   6.285%   $165.7302   $165.73   $165.75   $165.70  
  Purchase #6 $173.90   4.258%   $181.3047   $181.30   $181.30   $181.30  
  Purchase #7 $185.95   8.377%   $201.527   $201.53   $201.55   $201.50  
  7 purchase totals = $952.15       $1,023.0673   $1,023.07   $1,023.10   $1,023.00