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 $247.27   7.403%   $265.5754   $265.58   $265.60   $265.60  
  Purchase #2 $11.27   12.426%   $12.6704   $12.67   $12.65   $12.70  
  Purchase #3 $44.84   6.515%   $47.7613   $47.76   $47.75   $47.80  
  Purchase #4 $8.45   6.570%   $9.0052   $9.01   $9.00   $9.00  
  Purchase #5 $226.89   11.747%   $253.5428   $253.54   $253.55   $253.50  
  Purchase #6 $185.68   5.156%   $195.2537   $195.25   $195.25   $195.30  
  Purchase #7 $9.93   4.155%   $10.3426   $10.34   $10.35   $10.30  
  7 purchase totals = $734.33       $794.1514   $794.15   $794.15   $794.20