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 $58.97   10.104%   $64.9283   $64.93   $64.95   $64.90  
  Purchase #2 $228.98   7.274%   $245.636   $245.64   $245.65   $245.60  
  Purchase #3 $95.50   10.690%   $105.709   $105.71   $105.70   $105.70  
  Purchase #4 $242.42   10.633%   $268.1965   $268.20   $268.20   $268.20  
  Purchase #5 $75.75   4.771%   $79.364   $79.36   $79.35   $79.40  
  Purchase #6 $46.25   10.614%   $51.159   $51.16   $51.15   $51.20  
  Purchase #7 $245.30   9.380%   $268.3091   $268.31   $268.30   $268.30  
  7 purchase totals = $993.17       $1,083.3019   $1,083.31   $1,083.30   $1,083.30