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 $188.26   10.113%   $207.2987   $207.30   $207.30   $207.30  
  Purchase #2 $16.68   13.560%   $18.9418   $18.94   $18.95   $18.90  
  Purchase #3 $77.36   8.812%   $84.177   $84.18   $84.20   $84.20  
  Purchase #4 $214.39   5.632%   $226.4644   $226.46   $226.45   $226.50  
  Purchase #5 $218.91   6.272%   $232.64   $232.64   $232.65   $232.60  
  Purchase #6 $218.66   8.169%   $236.5223   $236.52   $236.50   $236.50  
  Purchase #7 $17.60   11.196%   $19.5705   $19.57   $19.55   $19.60  
  7 purchase totals = $951.86       $1,025.6147   $1,025.61   $1,025.60   $1,025.60