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 $174.54   6.569%   $186.0055   $186.01   $186.00   $186.00  
  Purchase #2 $17.59   7.469%   $18.9038   $18.90   $18.90   $18.90  
  Purchase #3 $188.68   7.275%   $202.4065   $202.41   $202.40   $202.40  
  Purchase #4 $163.54   12.355%   $183.7454   $183.75   $183.75   $183.70  
  Purchase #5 $35.52   11.298%   $39.533   $39.53   $39.55   $39.50  
  Purchase #6 $168.78   13.436%   $191.4573   $191.46   $191.45   $191.50  
  Purchase #7 $59.36   9.766%   $65.1571   $65.16   $65.15   $65.20  
  7 purchase totals = $808.01       $887.2086   $887.22   $887.20   $887.20