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 $163.61   8.164%   $176.9671   $176.97   $176.95   $177.00  
  Purchase #2 $218.51   11.667%   $244.0036   $244.00   $244.00   $244.00  
  Purchase #3 $200.89   7.383%   $215.7217   $215.72   $215.70   $215.70  
  Purchase #4 $184.53   8.481%   $200.18   $200.18   $200.20   $200.20  
  Purchase #5 $42.44   9.696%   $46.555   $46.56   $46.55   $46.60  
  Purchase #6 $190.27   11.807%   $212.7352   $212.74   $212.75   $212.70  
  Purchase #7 $74.68   11.462%   $83.2398   $83.24   $83.25   $83.20  
  7 purchase totals = $1,074.93       $1,179.4024   $1,179.41   $1,179.40   $1,179.40