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 $169.58   12.236%   $190.3298   $190.33   $190.35   $190.30  
  Purchase #2 $237.41   12.719%   $267.6062   $267.61   $267.60   $267.60  
  Purchase #3 $248.77   13.874%   $283.2843   $283.28   $283.30   $283.30  
  Purchase #4 $123.72   11.704%   $138.2002   $138.20   $138.20   $138.20  
  Purchase #5 $85.32   3.693%   $88.4709   $88.47   $88.45   $88.50  
  Purchase #6 $188.38   7.248%   $202.0338   $202.03   $202.05   $202.00  
  Purchase #7 $181.89   8.546%   $197.4343   $197.43   $197.45   $197.40  
  7 purchase totals = $1,235.07       $1,367.3595   $1,367.35   $1,367.40   $1,367.30