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 $232.51   12.342%   $261.2064   $261.21   $261.20   $261.20  
  Purchase #2 $70.91   9.457%   $77.616   $77.62   $77.60   $77.60  
  Purchase #3 $31.83   6.677%   $33.9553   $33.96   $33.95   $34.00  
  Purchase #4 $116.32   8.553%   $126.2688   $126.27   $126.25   $126.30  
  Purchase #5 $32.47   3.800%   $33.7039   $33.70   $33.70   $33.70  
  Purchase #6 $65.83   9.319%   $71.9647   $71.96   $71.95   $72.00  
  Purchase #7 $194.46   3.538%   $201.34   $201.34   $201.35   $201.30  
  7 purchase totals = $744.33       $806.0551   $806.06   $806.00   $806.10