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 $244.60   8.723%   $265.9365   $265.94   $265.95   $265.90  
  Purchase #2 $192.66   13.385%   $218.4475   $218.45   $218.45   $218.40  
  Purchase #3 $228.80   11.698%   $255.565   $255.57   $255.55   $255.60  
  Purchase #4 $153.31   7.616%   $164.9861   $164.99   $165.00   $165.00  
  Purchase #5 $74.41   9.542%   $81.5102   $81.51   $81.50   $81.50  
  Purchase #6 $58.73   6.660%   $62.6414   $62.64   $62.65   $62.60  
  Purchase #7 $88.73   8.193%   $95.9996   $96.00   $96.00   $96.00  
  7 purchase totals = $1,041.24       $1,145.0863   $1,145.10   $1,145.10   $1,145.00