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 $152.60   7.285%   $163.7169   $163.72   $163.70   $163.70  
  Purchase #2 $161.40   8.832%   $175.6548   $175.65   $175.65   $175.70  
  Purchase #3 $140.40   7.736%   $151.2613   $151.26   $151.25   $151.30  
  Purchase #4 $90.61   3.629%   $93.8982   $93.90   $93.90   $93.90  
  Purchase #5 $189.83   5.282%   $199.8568   $199.86   $199.85   $199.90  
  Purchase #6 $149.87   3.280%   $154.7857   $154.79   $154.80   $154.80  
  Purchase #7 $88.33   8.181%   $95.5563   $95.56   $95.55   $95.60  
  7 purchase totals = $973.04       $1,034.7300   $1,034.74   $1,034.70   $1,034.90