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 $166.82   8.638%   $181.2299   $181.23   $181.25   $181.20  
  Purchase #2 $88.81   5.340%   $93.5525   $93.55   $93.55   $93.60  
  Purchase #3 $175.82   11.646%   $196.296   $196.30   $196.30   $196.30  
  Purchase #4 $38.25   7.167%   $40.9914   $40.99   $41.00   $41.00  
  Purchase #5 $60.49   13.264%   $68.5134   $68.51   $68.50   $68.50  
  Purchase #6 $241.93   3.130%   $249.5024   $249.50   $249.50   $249.50  
  Purchase #7 $134.25   9.137%   $146.5164   $146.52   $146.50   $146.50  
  7 purchase totals = $906.37       $976.6020   $976.60   $976.60   $976.60