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 $222.26   10.845%   $246.3641   $246.36   $246.35   $246.40  
  Purchase #2 $186.51   5.526%   $196.8165   $196.82   $196.80   $196.80  
  Purchase #3 $82.48   13.489%   $93.6057   $93.61   $93.60   $93.60  
  Purchase #4 $204.77   4.760%   $214.5171   $214.52   $214.50   $214.50  
  Purchase #5 $5.67   6.719%   $6.051   $6.05   $6.05   $6.10  
  Purchase #6 $70.67   8.764%   $76.8635   $76.86   $76.85   $76.90  
  Purchase #7 $22.81   5.208%   $23.9979   $24.00   $24.00   $24.00  
  7 purchase totals = $795.17       $858.2158   $858.22   $858.15   $858.30