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 $186.82   8.658%   $202.9949   $202.99   $203.00   $203.00  
  Purchase #2 $114.34   8.794%   $124.3951   $124.40   $124.40   $124.40  
  Purchase #3 $74.78   13.500%   $84.8753   $84.88   $84.90   $84.90  
  Purchase #4 $116.40   13.314%   $131.8975   $131.90   $131.90   $131.90  
  Purchase #5 $167.70   9.428%   $183.5108   $183.51   $183.50   $183.50  
  Purchase #6 $85.44   11.854%   $95.5681   $95.57   $95.55   $95.60  
  Purchase #7 $158.72   10.279%   $175.0348   $175.03   $175.05   $175.00  
  7 purchase totals = $904.20       $998.2765   $998.28   $998.30   $998.30