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 $52.28   5.588%   $55.2014   $55.20   $55.20   $55.20  
  Purchase #2 $98.86   12.396%   $111.1147   $111.11   $111.10   $111.10  
  Purchase #3 $157.77   5.147%   $165.8904   $165.89   $165.90   $165.90  
  Purchase #4 $240.45   10.363%   $265.3678   $265.37   $265.35   $265.40  
  Purchase #5 $184.92   7.284%   $198.3896   $198.39   $198.40   $198.40  
  Purchase #6 $114.35   4.179%   $119.1287   $119.13   $119.15   $119.10  
  Purchase #7 $113.65   7.563%   $122.2453   $122.25   $122.25   $122.20  
  7 purchase totals = $962.28       $1,037.3379   $1,037.34   $1,037.35   $1,037.30