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 $207.91   8.513%   $225.6094   $225.61   $225.60   $225.60  
  Purchase #2 $68.40   10.181%   $75.3638   $75.36   $75.35   $75.40  
  Purchase #3 $194.94   9.760%   $213.9661   $213.97   $213.95   $214.00  
  Purchase #4 $13.61   7.117%   $14.5786   $14.58   $14.60   $14.60  
  Purchase #5 $225.55   11.406%   $251.2762   $251.28   $251.30   $251.30  
  Purchase #6 $187.65   9.628%   $205.7169   $205.72   $205.70   $205.70  
  Purchase #7 $110.40   3.269%   $114.009   $114.01   $114.00   $114.00  
  7 purchase totals = $1,008.46       $1,100.5200   $1,100.53   $1,100.50   $1,100.60