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 $163.86   11.684%   $183.0054   $183.01   $183.00   $183.00  
  Purchase #2 $125.47   9.391%   $137.2529   $137.25   $137.25   $137.30  
  Purchase #3 $167.84   8.617%   $182.3028   $182.30   $182.30   $182.30  
  Purchase #4 $214.30   3.720%   $222.272   $222.27   $222.25   $222.30  
  Purchase #5 $121.33   13.466%   $137.6683   $137.67   $137.65   $137.70  
  Purchase #6 $184.90   3.623%   $191.5989   $191.60   $191.60   $191.60  
  Purchase #7 $74.31   9.658%   $81.4869   $81.49   $81.50   $81.50  
  7 purchase totals = $1,052.01       $1,135.5872   $1,135.59   $1,135.55   $1,135.70