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 $52.48   12.459%   $59.0185   $59.02   $59.00   $59.00  
  Purchase #2 $195.32   4.517%   $204.1426   $204.14   $204.15   $204.10  
  Purchase #3 $214.33   8.648%   $232.8653   $232.87   $232.85   $232.90  
  Purchase #4 $20.38   13.187%   $23.0675   $23.07   $23.05   $23.10  
  Purchase #5 $62.46   13.575%   $70.9389   $70.94   $70.95   $70.90  
  Purchase #6 $81.40   11.557%   $90.8074   $90.81   $90.80   $90.80  
  Purchase #7 $118.35   5.363%   $124.6971   $124.70   $124.70   $124.70  
  7 purchase totals = $744.72       $805.5373   $805.55   $805.50   $805.50