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 $187.27   5.201%   $197.0099   $197.01   $197.00   $197.00  
  Purchase #2 $46.71   13.413%   $52.9752   $52.98   $53.00   $53.00  
  Purchase #3 $226.87   5.487%   $239.3184   $239.32   $239.30   $239.30  
  Purchase #4 $62.57   12.699%   $70.5158   $70.52   $70.50   $70.50  
  Purchase #5 $164.94   6.405%   $175.5044   $175.50   $175.50   $175.50  
  Purchase #6 $230.63   7.577%   $248.1048   $248.10   $248.10   $248.10  
  Purchase #7 $6.92   12.684%   $7.7977   $7.80   $7.80   $7.80  
  7 purchase totals = $925.91       $991.2262   $991.23   $991.20   $991.20