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 $113.98   11.420%   $126.9965   $127.00   $127.00   $127.00  
  Purchase #2 $24.86   5.700%   $26.277   $26.28   $26.30   $26.30  
  Purchase #3 $81.45   4.583%   $85.1829   $85.18   $85.20   $85.20  
  Purchase #4 $157.38   3.857%   $163.4501   $163.45   $163.45   $163.50  
  Purchase #5 $38.31   12.347%   $43.0401   $43.04   $43.05   $43.00  
  Purchase #6 $185.99   11.685%   $207.7229   $207.72   $207.70   $207.70  
  Purchase #7 $148.81   4.690%   $155.7892   $155.79   $155.80   $155.80  
  7 purchase totals = $750.78       $808.4587   $808.46   $808.50   $808.50