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 $29.66   11.731%   $33.1394   $33.14   $33.15   $33.10  
  Purchase #2 $246.59   7.577%   $265.2741   $265.27   $265.25   $265.30  
  Purchase #3 $102.40   9.497%   $112.1249   $112.12   $112.10   $112.10  
  Purchase #4 $218.33   9.505%   $239.0823   $239.08   $239.10   $239.10  
  Purchase #5 $118.28   9.454%   $129.4622   $129.46   $129.45   $129.50  
  Purchase #6 $167.92   13.235%   $190.1442   $190.14   $190.15   $190.10  
  Purchase #7 $46.76   10.676%   $51.7521   $51.75   $51.75   $51.80  
  7 purchase totals = $929.94       $1,020.9792   $1,020.96   $1,020.95   $1,021.00