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 $82.70   5.197%   $86.9979   $87.00   $87.00   $87.00  
  Purchase #2 $183.78   9.851%   $201.8842   $201.88   $201.90   $201.90  
  Purchase #3 $237.53   6.299%   $252.492   $252.49   $252.50   $252.50  
  Purchase #4 $224.52   6.550%   $239.2261   $239.23   $239.25   $239.20  
  Purchase #5 $11.41   7.357%   $12.2494   $12.25   $12.25   $12.20  
  Purchase #6 $247.34   7.484%   $265.8509   $265.85   $265.85   $265.90  
  Purchase #7 $80.36   6.129%   $85.2853   $85.29   $85.30   $85.30  
  7 purchase totals = $1,067.64       $1,143.9858   $1,143.99   $1,144.05   $1,144.00