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 $161.42   13.488%   $183.1923   $183.19   $183.20   $183.20  
  Purchase #2 $92.57   5.481%   $97.6438   $97.64   $97.65   $97.60  
  Purchase #3 $34.89   7.119%   $37.3738   $37.37   $37.35   $37.40  
  Purchase #4 $174.59   10.534%   $192.9813   $192.98   $193.00   $193.00  
  Purchase #5 $248.94   6.782%   $265.8231   $265.82   $265.80   $265.80  
  Purchase #6 $41.65   7.481%   $44.7658   $44.77   $44.75   $44.80  
  Purchase #7 $122.98   12.614%   $138.4927   $138.49   $138.50   $138.50  
  7 purchase totals = $877.04       $960.2728   $960.26   $960.25   $960.30