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 $57.85   3.788%   $60.0414   $60.04   $60.05   $60.00  
  Purchase #2 $248.47   11.413%   $276.8279   $276.83   $276.85   $276.80  
  Purchase #3 $147.81   3.688%   $153.2612   $153.26   $153.25   $153.30  
  Purchase #4 $228.92   9.581%   $250.8528   $250.85   $250.85   $250.90  
  Purchase #5 $5.58   7.855%   $6.0183   $6.02   $6.00   $6.00  
  Purchase #6 $101.31   6.627%   $108.0238   $108.02   $108.00   $108.00  
  Purchase #7 $169.27   11.597%   $188.9002   $188.90   $188.90   $188.90  
  7 purchase totals = $959.21       $1,043.9256   $1,043.92   $1,043.90   $1,043.90