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 $33.40   5.716%   $35.3091   $35.31   $35.30   $35.30  
  Purchase #2 $223.49   3.155%   $230.5411   $230.54   $230.55   $230.50  
  Purchase #3 $35.62   6.808%   $38.045   $38.05   $38.05   $38.00  
  Purchase #4 $169.41   9.670%   $185.7919   $185.79   $185.80   $185.80  
  Purchase #5 $100.52   6.706%   $107.2609   $107.26   $107.25   $107.30  
  Purchase #6 $112.72   12.811%   $127.1606   $127.16   $127.15   $127.20  
  Purchase #7 $211.71   11.793%   $236.677   $236.68   $236.70   $236.70  
  7 purchase totals = $886.87       $960.7856   $960.79   $960.80   $960.80