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 $234.96   13.617%   $266.9545   $266.95   $266.95   $267.00  
  Purchase #2 $134.80   9.133%   $147.1113   $147.11   $147.10   $147.10  
  Purchase #3 $218.60   6.199%   $232.151   $232.15   $232.15   $232.20  
  Purchase #4 $134.25   7.533%   $144.3631   $144.36   $144.35   $144.40  
  Purchase #5 $108.93   9.118%   $118.8622   $118.86   $118.85   $118.90  
  Purchase #6 $68.63   7.215%   $73.5817   $73.58   $73.60   $73.60  
  Purchase #7 $81.70   11.202%   $90.852   $90.85   $90.85   $90.90  
  7 purchase totals = $981.87       $1,073.8758   $1,073.86   $1,073.85   $1,074.10