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 $245.93   9.681%   $269.7385   $269.74   $269.75   $269.70  
  Purchase #2 $80.29   12.335%   $90.1938   $90.19   $90.20   $90.20  
  Purchase #3 $84.74   9.463%   $92.7589   $92.76   $92.75   $92.80  
  Purchase #4 $127.57   13.332%   $144.5776   $144.58   $144.60   $144.60  
  Purchase #5 $100.44   13.533%   $114.0325   $114.03   $114.05   $114.00  
  Purchase #6 $145.54   4.437%   $151.9976   $152.00   $152.00   $152.00  
  Purchase #7 $149.64   9.222%   $163.4398   $163.44   $163.45   $163.40  
  7 purchase totals = $934.15       $1,026.7387   $1,026.74   $1,026.80   $1,026.70