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 $114.62   10.164%   $126.27   $126.27   $126.25   $126.30  
  Purchase #2 $169.37   12.619%   $190.7428   $190.74   $190.75   $190.70  
  Purchase #3 $60.64   13.107%   $68.5881   $68.59   $68.60   $68.60  
  Purchase #4 $125.77   13.826%   $143.159   $143.16   $143.15   $143.20  
  Purchase #5 $163.30   7.647%   $175.7876   $175.79   $175.80   $175.80  
  Purchase #6 $232.83   5.414%   $245.4354   $245.44   $245.45   $245.40  
  Purchase #7 $242.29   8.787%   $263.58   $263.58   $263.60   $263.60  
  7 purchase totals = $1,108.82       $1,213.5629   $1,213.57   $1,213.60   $1,213.60