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 $242.71   6.576%   $258.6706   $258.67   $258.65   $258.70  
  Purchase #2 $61.60   5.236%   $64.8254   $64.83   $64.85   $64.80  
  Purchase #3 $62.54   9.762%   $68.6452   $68.65   $68.65   $68.60  
  Purchase #4 $25.55   4.213%   $26.6264   $26.63   $26.65   $26.60  
  Purchase #5 $186.49   7.523%   $200.5196   $200.52   $200.50   $200.50  
  Purchase #6 $241.42   4.472%   $252.2163   $252.22   $252.20   $252.20  
  Purchase #7 $200.74   4.184%   $209.139   $209.14   $209.15   $209.10  
  7 purchase totals = $1,021.05       $1,080.6425   $1,080.66   $1,080.65   $1,080.50