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 $168.61   10.754%   $186.7423   $186.74   $186.75   $186.70  
  Purchase #2 $80.29   8.360%   $87.0022   $87.00   $87.00   $87.00  
  Purchase #3 $24.96   6.549%   $26.5946   $26.59   $26.60   $26.60  
  Purchase #4 $208.68   12.501%   $234.7671   $234.77   $234.75   $234.80  
  Purchase #5 $136.86   11.844%   $153.0697   $153.07   $153.05   $153.10  
  Purchase #6 $122.34   5.201%   $128.7029   $128.70   $128.70   $128.70  
  Purchase #7 $65.69   8.435%   $71.231   $71.23   $71.25   $71.20  
  7 purchase totals = $807.43       $888.1098   $888.10   $888.10   $888.10