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 $216.49   13.625%   $245.9868   $245.99   $246.00   $246.00  
  Purchase #2 $117.67   5.774%   $124.4643   $124.46   $124.45   $124.50  
  Purchase #3 $63.59   4.339%   $66.3492   $66.35   $66.35   $66.30  
  Purchase #4 $5.40   10.568%   $5.9707   $5.97   $5.95   $6.00  
  Purchase #5 $165.27   8.816%   $179.8402   $179.84   $179.85   $179.80  
  Purchase #6 $103.43   5.274%   $108.8849   $108.88   $108.90   $108.90  
  Purchase #7 $190.36   7.386%   $204.42   $204.42   $204.40   $204.40  
  7 purchase totals = $862.21       $935.9161   $935.91   $935.90   $935.90