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 $38.76   4.806%   $40.6228   $40.62   $40.60   $40.60  
  Purchase #2 $41.41   10.236%   $45.6487   $45.65   $45.65   $45.60  
  Purchase #3 $241.89   12.524%   $272.1843   $272.18   $272.20   $272.20  
  Purchase #4 $216.98   3.575%   $224.737   $224.74   $224.75   $224.70  
  Purchase #5 $235.99   13.123%   $266.959   $266.96   $266.95   $267.00  
  Purchase #6 $53.55   5.215%   $56.3426   $56.34   $56.35   $56.30  
  Purchase #7 $179.38   3.781%   $186.1624   $186.16   $186.15   $186.20  
  7 purchase totals = $1,007.96       $1,092.6568   $1,092.65   $1,092.65   $1,092.60