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 $249.55   5.693%   $263.7569   $263.76   $263.75   $263.80  
  Purchase #2 $111.39   3.103%   $114.8464   $114.85   $114.85   $114.80  
  Purchase #3 $115.76   4.219%   $120.6439   $120.64   $120.65   $120.60  
  Purchase #4 $62.30   13.597%   $70.7709   $70.77   $70.75   $70.80  
  Purchase #5 $190.51   3.495%   $197.1683   $197.17   $197.15   $197.20  
  Purchase #6 $155.49   12.607%   $175.0926   $175.09   $175.10   $175.10  
  Purchase #7 $83.48   6.171%   $88.6316   $88.63   $88.65   $88.60  
  7 purchase totals = $968.48       $1,030.9106   $1,030.91   $1,030.90   $1,030.90