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 $191.28   10.311%   $211.0029   $211.00   $211.00   $211.00  
  Purchase #2 $87.90   9.205%   $95.9912   $95.99   $96.00   $96.00  
  Purchase #3 $105.37   13.338%   $119.4243   $119.42   $119.40   $119.40  
  Purchase #4 $43.58   5.786%   $46.1015   $46.10   $46.10   $46.10  
  Purchase #5 $45.43   8.528%   $49.3043   $49.30   $49.30   $49.30  
  Purchase #6 $61.67   11.670%   $68.8669   $68.87   $68.85   $68.90  
  Purchase #7 $233.71   4.108%   $243.3108   $243.31   $243.30   $243.30  
  7 purchase totals = $768.94       $834.0019   $833.99   $833.95   $834.00