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 $67.61   12.780%   $76.2506   $76.25   $76.25   $76.30  
  Purchase #2 $50.91   9.720%   $55.8585   $55.86   $55.85   $55.90  
  Purchase #3 $123.69   11.871%   $138.3732   $138.37   $138.35   $138.40  
  Purchase #4 $231.90   10.859%   $257.082   $257.08   $257.10   $257.10  
  Purchase #5 $163.31   13.341%   $185.0972   $185.10   $185.10   $185.10  
  Purchase #6 $84.76   8.488%   $91.9544   $91.95   $91.95   $92.00  
  Purchase #7 $239.37   3.352%   $247.3937   $247.39   $247.40   $247.40  
  7 purchase totals = $961.55       $1,052.0096   $1,052.00   $1,052.00   $1,052.20