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 $207.51   13.462%   $235.445   $235.45   $235.45   $235.40  
  Purchase #2 $64.43   6.118%   $68.3718   $68.37   $68.35   $68.40  
  Purchase #3 $58.32   10.826%   $64.6337   $64.63   $64.65   $64.60  
  Purchase #4 $219.30   7.451%   $235.64   $235.64   $235.65   $235.60  
  Purchase #5 $135.90   13.676%   $154.4857   $154.49   $154.50   $154.50  
  Purchase #6 $227.49   6.420%   $242.0949   $242.09   $242.10   $242.10  
  Purchase #7 $70.91   8.859%   $77.1919   $77.19   $77.20   $77.20  
  7 purchase totals = $983.86       $1,077.8630   $1,077.86   $1,077.90   $1,077.80