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 $195.75   3.472%   $202.5464   $202.55   $202.55   $202.50  
  Purchase #2 $163.69   8.779%   $178.0603   $178.06   $178.05   $178.10  
  Purchase #3 $136.44   9.874%   $149.9121   $149.91   $149.90   $149.90  
  Purchase #4 $111.61   9.424%   $122.1281   $122.13   $122.15   $122.10  
  Purchase #5 $23.98   4.608%   $25.085   $25.09   $25.10   $25.10  
  Purchase #6 $26.43   9.659%   $28.9829   $28.98   $29.00   $29.00  
  Purchase #7 $227.26   9.144%   $248.0407   $248.04   $248.05   $248.00  
  7 purchase totals = $885.16       $954.7555   $954.76   $954.80   $954.70