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 $219.80   13.224%   $248.8664   $248.87   $248.85   $248.90  
  Purchase #2 $142.61   8.452%   $154.6634   $154.66   $154.65   $154.70  
  Purchase #3 $222.29   12.679%   $250.4741   $250.47   $250.45   $250.50  
  Purchase #4 $157.33   5.243%   $165.5788   $165.58   $165.60   $165.60  
  Purchase #5 $105.68   11.834%   $118.1862   $118.19   $118.20   $118.20  
  Purchase #6 $137.42   9.827%   $150.9243   $150.92   $150.90   $150.90  
  Purchase #7 $35.91   4.812%   $37.638   $37.64   $37.65   $37.60  
  7 purchase totals = $1,021.04       $1,126.3312   $1,126.33   $1,126.30   $1,126.40