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 $224.84   12.864%   $253.7634   $253.76   $253.75   $253.80  
  Purchase #2 $88.75   7.770%   $95.6459   $95.65   $95.65   $95.60  
  Purchase #3 $81.99   4.358%   $85.5631   $85.56   $85.55   $85.60  
  Purchase #4 $208.89   4.653%   $218.6097   $218.61   $218.60   $218.60  
  Purchase #5 $249.58   8.335%   $270.3825   $270.38   $270.40   $270.40  
  Purchase #6 $138.85   8.424%   $150.5467   $150.55   $150.55   $150.50  
  Purchase #7 $107.38   10.293%   $118.4326   $118.43   $118.45   $118.40  
  7 purchase totals = $1,100.28       $1,192.9439   $1,192.94   $1,192.95   $1,192.90