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 $242.83   7.302%   $260.5614   $260.56   $260.55   $260.60  
  Purchase #2 $102.58   6.421%   $109.1667   $109.17   $109.15   $109.20  
  Purchase #3 $83.50   13.560%   $94.8226   $94.82   $94.80   $94.80  
  Purchase #4 $35.64   3.345%   $36.8322   $36.83   $36.85   $36.80  
  Purchase #5 $198.25   8.107%   $214.3221   $214.32   $214.30   $214.30  
  Purchase #6 $87.86   4.156%   $91.5115   $91.51   $91.50   $91.50  
  Purchase #7 $241.52   8.386%   $261.7739   $261.77   $261.75   $261.80  
  7 purchase totals = $992.18       $1,068.9904   $1,068.98   $1,068.90   $1,069.00