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 $95.50   6.566%   $101.7705   $101.77   $101.75   $101.80  
  Purchase #2 $120.59   6.617%   $128.5694   $128.57   $128.55   $128.60  
  Purchase #3 $102.96   6.439%   $109.5896   $109.59   $109.60   $109.60  
  Purchase #4 $165.99   5.721%   $175.4863   $175.49   $175.50   $175.50  
  Purchase #5 $102.42   11.297%   $113.9904   $113.99   $114.00   $114.00  
  Purchase #6 $143.39   6.814%   $153.1606   $153.16   $153.15   $153.20  
  Purchase #7 $212.80   5.556%   $224.6232   $224.62   $224.60   $224.60  
  7 purchase totals = $943.65       $1,007.1900   $1,007.19   $1,007.15   $1,007.30