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 $84.74   11.577%   $94.5503   $94.55   $94.55   $94.60  
  Purchase #2 $56.85   10.397%   $62.7607   $62.76   $62.75   $62.80  
  Purchase #3 $122.76   5.363%   $129.3436   $129.34   $129.35   $129.30  
  Purchase #4 $243.94   5.414%   $257.1469   $257.15   $257.15   $257.10  
  Purchase #5 $91.25   3.634%   $94.566   $94.57   $94.55   $94.60  
  Purchase #6 $247.95   3.376%   $256.3208   $256.32   $256.30   $256.30  
  Purchase #7 $158.61   6.580%   $169.0465   $169.05   $169.05   $169.00  
  7 purchase totals = $1,006.10       $1,063.7348   $1,063.74   $1,063.70   $1,063.70