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 $42.48   4.204%   $44.2659   $44.27   $44.25   $44.30  
  Purchase #2 $107.79   12.433%   $121.1915   $121.19   $121.20   $121.20  
  Purchase #3 $108.30   11.852%   $121.1357   $121.14   $121.15   $121.10  
  Purchase #4 $193.49   4.152%   $201.5237   $201.52   $201.50   $201.50  
  Purchase #5 $117.94   6.344%   $125.4221   $125.42   $125.40   $125.40  
  Purchase #6 $240.40   11.862%   $268.9162   $268.92   $268.90   $268.90  
  Purchase #7 $32.25   5.426%   $33.9999   $34.00   $34.00   $34.00  
  7 purchase totals = $842.65       $916.4550   $916.46   $916.40   $916.40