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 $177.28   8.298%   $191.9907   $191.99   $192.00   $192.00  
  Purchase #2 $30.75   12.664%   $34.6442   $34.64   $34.65   $34.60  
  Purchase #3 $108.56   10.450%   $119.9045   $119.90   $119.90   $119.90  
  Purchase #4 $245.86   3.867%   $255.3674   $255.37   $255.35   $255.40  
  Purchase #5 $155.99   12.438%   $175.392   $175.39   $175.40   $175.40  
  Purchase #6 $128.81   13.265%   $145.8966   $145.90   $145.90   $145.90  
  Purchase #7 $127.59   11.471%   $142.2258   $142.23   $142.25   $142.20  
  7 purchase totals = $974.84       $1,065.4212   $1,065.42   $1,065.45   $1,065.40