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 $78.55   10.291%   $86.6336   $86.63   $86.65   $86.60  
  Purchase #2 $150.95   10.610%   $166.9658   $166.97   $166.95   $167.00  
  Purchase #3 $115.91   5.836%   $122.6745   $122.67   $122.65   $122.70  
  Purchase #4 $241.79   9.301%   $264.2789   $264.28   $264.30   $264.30  
  Purchase #5 $84.36   10.391%   $93.1258   $93.13   $93.15   $93.10  
  Purchase #6 $166.55   13.827%   $189.5789   $189.58   $189.60   $189.60  
  Purchase #7 $202.59   13.296%   $229.5264   $229.53   $229.55   $229.50  
  7 purchase totals = $1,040.70       $1,152.7839   $1,152.79   $1,152.85   $1,152.80