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 $229.73   8.401%   $249.0296   $249.03   $249.05   $249.00  
  Purchase #2 $183.86   4.664%   $192.4352   $192.44   $192.45   $192.40  
  Purchase #3 $157.80   12.204%   $177.0579   $177.06   $177.05   $177.10  
  Purchase #4 $52.27   5.395%   $55.09   $55.09   $55.10   $55.10  
  Purchase #5 $149.52   10.787%   $165.6487   $165.65   $165.65   $165.60  
  Purchase #6 $240.45   9.132%   $262.4079   $262.41   $262.40   $262.40  
  Purchase #7 $219.29   10.596%   $242.526   $242.53   $242.55   $242.50  
  7 purchase totals = $1,232.92       $1,344.1953   $1,344.21   $1,344.25   $1,344.10