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 $92.32   10.476%   $101.9914   $101.99   $102.00   $102.00  
  Purchase #2 $216.53   3.634%   $224.3987   $224.40   $224.40   $224.40  
  Purchase #3 $228.96   12.368%   $257.2778   $257.28   $257.30   $257.30  
  Purchase #4 $113.58   8.874%   $123.6591   $123.66   $123.65   $123.70  
  Purchase #5 $220.91   5.379%   $232.7927   $232.79   $232.80   $232.80  
  Purchase #6 $50.79   8.802%   $55.2605   $55.26   $55.25   $55.30  
  Purchase #7 $246.36   8.749%   $267.914   $267.91   $267.90   $267.90  
  7 purchase totals = $1,169.45       $1,263.2942   $1,263.29   $1,263.30   $1,263.40