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 $84.63   10.616%   $93.6143   $93.61   $93.60   $93.60  
  Purchase #2 $206.65   8.780%   $224.7939   $224.79   $224.80   $224.80  
  Purchase #3 $191.60   11.762%   $214.136   $214.14   $214.15   $214.10  
  Purchase #4 $208.66   12.486%   $234.7133   $234.71   $234.70   $234.70  
  Purchase #5 $134.63   9.668%   $147.646   $147.65   $147.65   $147.60  
  Purchase #6 $169.57   12.330%   $190.478   $190.48   $190.50   $190.50  
  Purchase #7 $70.91   7.444%   $76.1885   $76.19   $76.20   $76.20  
  7 purchase totals = $1,066.65       $1,181.5700   $1,181.57   $1,181.60   $1,181.50