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 $32.70   10.281%   $36.0619   $36.06   $36.05   $36.10  
  Purchase #2 $192.33   8.705%   $209.0723   $209.07   $209.05   $209.10  
  Purchase #3 $229.80   8.283%   $248.8343   $248.83   $248.85   $248.80  
  Purchase #4 $93.26   7.166%   $99.943   $99.94   $99.95   $99.90  
  Purchase #5 $233.94   5.544%   $246.9096   $246.91   $246.90   $246.90  
  Purchase #6 $49.49   5.646%   $52.2842   $52.28   $52.30   $52.30  
  Purchase #7 $231.84   3.467%   $239.8779   $239.88   $239.90   $239.90  
  7 purchase totals = $1,063.36       $1,132.9832   $1,132.97   $1,133.00   $1,133.00