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 $143.43   6.110%   $152.1936   $152.19   $152.20   $152.20  
  Purchase #2 $240.75   12.604%   $271.0941   $271.09   $271.10   $271.10  
  Purchase #3 $229.25   10.627%   $253.6124   $253.61   $253.60   $253.60  
  Purchase #4 $167.97   7.418%   $180.43   $180.43   $180.45   $180.40  
  Purchase #5 $35.84   8.717%   $38.9642   $38.96   $38.95   $39.00  
  Purchase #6 $164.26   11.133%   $182.5471   $182.55   $182.55   $182.50  
  Purchase #7 $245.59   8.646%   $266.8237   $266.82   $266.80   $266.80  
  7 purchase totals = $1,227.09       $1,345.6651   $1,345.65   $1,345.65   $1,345.60