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 $54.79   6.772%   $58.5004   $58.50   $58.50   $58.50  
  Purchase #2 $222.75   12.792%   $251.2442   $251.24   $251.25   $251.20  
  Purchase #3 $184.37   4.498%   $192.663   $192.66   $192.65   $192.70  
  Purchase #4 $181.33   11.734%   $202.6073   $202.61   $202.60   $202.60  
  Purchase #5 $87.46   13.507%   $99.2732   $99.27   $99.25   $99.30  
  Purchase #6 $150.46   8.725%   $163.5876   $163.59   $163.60   $163.60  
  Purchase #7 $193.85   6.621%   $206.6848   $206.68   $206.70   $206.70  
  7 purchase totals = $1,075.01       $1,174.5605   $1,174.55   $1,174.55   $1,174.60