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 $63.75   5.319%   $67.1409   $67.14   $67.15   $67.10  
  Purchase #2 $11.60   13.107%   $13.1204   $13.12   $13.10   $13.10  
  Purchase #3 $220.89   9.346%   $241.5344   $241.53   $241.55   $241.50  
  Purchase #4 $77.51   5.632%   $81.8754   $81.88   $81.90   $81.90  
  Purchase #5 $26.92   7.592%   $28.9638   $28.96   $28.95   $29.00  
  Purchase #6 $204.73   8.729%   $222.6009   $222.60   $222.60   $222.60  
  Purchase #7 $214.66   12.261%   $240.9795   $240.98   $241.00   $241.00  
  7 purchase totals = $820.06       $896.2153   $896.21   $896.25   $896.20