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 $219.97   6.342%   $233.9205   $233.92   $233.90   $233.90  
  Purchase #2 $184.97   4.638%   $193.5489   $193.55   $193.55   $193.50  
  Purchase #3 $58.48   3.776%   $60.6882   $60.69   $60.70   $60.70  
  Purchase #4 $244.55   6.497%   $260.4384   $260.44   $260.45   $260.40  
  Purchase #5 $230.41   5.158%   $242.2945   $242.29   $242.30   $242.30  
  Purchase #6 $13.92   5.320%   $14.6605   $14.66   $14.65   $14.70  
  Purchase #7 $39.84   8.561%   $43.2507   $43.25   $43.25   $43.30  
  7 purchase totals = $992.14       $1,048.8017   $1,048.80   $1,048.80   $1,048.80