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 $149.85   11.543%   $167.1472   $167.15   $167.15   $167.10  
  Purchase #2 $113.74   10.237%   $125.3836   $125.38   $125.40   $125.40  
  Purchase #3 $173.31   11.705%   $193.5959   $193.60   $193.60   $193.60  
  Purchase #4 $208.60   5.835%   $220.7718   $220.77   $220.75   $220.80  
  Purchase #5 $241.70   9.756%   $265.2803   $265.28   $265.30   $265.30  
  Purchase #6 $142.57   7.346%   $153.0432   $153.04   $153.05   $153.00  
  Purchase #7 $219.35   3.367%   $226.7355   $226.74   $226.75   $226.70  
  7 purchase totals = $1,249.12       $1,351.9575   $1,351.96   $1,352.00   $1,351.90