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 $248.93   9.453%   $272.4614   $272.46   $272.45   $272.50  
  Purchase #2 $150.98   9.852%   $165.8545   $165.85   $165.85   $165.90  
  Purchase #3 $188.59   3.630%   $195.4358   $195.44   $195.45   $195.40  
  Purchase #4 $120.39   7.366%   $129.2579   $129.26   $129.25   $129.30  
  Purchase #5 $88.72   11.433%   $98.8634   $98.86   $98.85   $98.90  
  Purchase #6 $81.41   9.737%   $89.3369   $89.34   $89.35   $89.30  
  Purchase #7 $109.57   10.483%   $121.0562   $121.06   $121.05   $121.10  
  7 purchase totals = $988.59       $1,072.2661   $1,072.27   $1,072.25   $1,072.40