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 $175.49   4.259%   $182.9641   $182.96   $182.95   $183.00  
  Purchase #2 $211.34   11.181%   $234.9699   $234.97   $234.95   $235.00  
  Purchase #3 $185.55   13.446%   $210.4991   $210.50   $210.50   $210.50  
  Purchase #4 $46.33   10.500%   $51.1947   $51.19   $51.20   $51.20  
  Purchase #5 $192.85   10.411%   $212.9276   $212.93   $212.95   $212.90  
  Purchase #6 $159.85   12.362%   $179.6107   $179.61   $179.60   $179.60  
  Purchase #7 $127.61   6.391%   $135.7656   $135.77   $135.75   $135.80  
  7 purchase totals = $1,099.02       $1,207.9317   $1,207.93   $1,207.90   $1,208.00