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 $44.44   10.272%   $49.0049   $49.00   $49.00   $49.00  
  Purchase #2 $239.61   13.254%   $271.3679   $271.37   $271.35   $271.40  
  Purchase #3 $189.47   8.541%   $205.6526   $205.65   $205.65   $205.70  
  Purchase #4 $49.98   8.589%   $54.2728   $54.27   $54.25   $54.30  
  Purchase #5 $103.54   9.731%   $113.6155   $113.62   $113.60   $113.60  
  Purchase #6 $161.99   10.565%   $179.1042   $179.10   $179.10   $179.10  
  Purchase #7 $144.35   13.407%   $163.703   $163.70   $163.70   $163.70  
  7 purchase totals = $933.38       $1,036.7209   $1,036.71   $1,036.65   $1,036.80