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 $238.33   8.673%   $259.0004   $259.00   $259.00   $259.00  
  Purchase #2 $58.71   12.391%   $65.9848   $65.98   $66.00   $66.00  
  Purchase #3 $162.43   7.298%   $174.2841   $174.28   $174.30   $174.30  
  Purchase #4 $200.75   6.579%   $213.9573   $213.96   $213.95   $214.00  
  Purchase #5 $156.70   12.434%   $176.1841   $176.18   $176.20   $176.20  
  Purchase #6 $238.71   12.629%   $268.8567   $268.86   $268.85   $268.90  
  Purchase #7 $150.37   10.433%   $166.0581   $166.06   $166.05   $166.10  
  7 purchase totals = $1,206.00       $1,324.3255   $1,324.32   $1,324.35   $1,324.50