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 $150.74   6.484%   $160.514   $160.51   $160.50   $160.50  
  Purchase #2 $74.30   10.357%   $81.9953   $82.00   $82.00   $82.00  
  Purchase #3 $103.31   9.719%   $113.3507   $113.35   $113.35   $113.40  
  Purchase #4 $213.37   5.400%   $224.892   $224.89   $224.90   $224.90  
  Purchase #5 $127.27   6.656%   $135.7411   $135.74   $135.75   $135.70  
  Purchase #6 $47.78   4.681%   $50.0166   $50.02   $50.00   $50.00  
  Purchase #7 $233.37   9.470%   $255.4701   $255.47   $255.45   $255.50  
  7 purchase totals = $950.14       $1,021.9798   $1,021.98   $1,021.95   $1,022.00