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 $85.89   11.566%   $95.824   $95.82   $95.80   $95.80  
  Purchase #2 $62.51   9.570%   $68.4922   $68.49   $68.50   $68.50  
  Purchase #3 $91.29   5.851%   $96.6314   $96.63   $96.65   $96.60  
  Purchase #4 $77.41   5.856%   $81.9431   $81.94   $81.95   $81.90  
  Purchase #5 $235.81   10.190%   $259.839   $259.84   $259.85   $259.80  
  Purchase #6 $188.94   9.562%   $207.0064   $207.01   $207.00   $207.00  
  Purchase #7 $59.51   4.231%   $62.0279   $62.03   $62.05   $62.00  
  7 purchase totals = $801.36       $871.7640   $871.76   $871.80   $871.60