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 $54.59   11.721%   $60.9885   $60.99   $61.00   $61.00  
  Purchase #2 $103.94   4.508%   $108.6256   $108.63   $108.65   $108.60  
  Purchase #3 $103.50   4.520%   $108.1782   $108.18   $108.20   $108.20  
  Purchase #4 $224.61   7.205%   $240.7932   $240.79   $240.80   $240.80  
  Purchase #5 $153.97   3.427%   $159.2466   $159.25   $159.25   $159.20  
  Purchase #6 $122.41   5.201%   $128.7765   $128.78   $128.80   $128.80  
  Purchase #7 $25.74   3.524%   $26.6471   $26.65   $26.65   $26.60  
  7 purchase totals = $788.76       $833.2557   $833.27   $833.35   $833.20