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 $32.75   5.168%   $34.4425   $34.44   $34.45   $34.40  
  Purchase #2 $174.95   6.813%   $186.8693   $186.87   $186.85   $186.90  
  Purchase #3 $200.83   12.345%   $225.6225   $225.62   $225.60   $225.60  
  Purchase #4 $203.42   11.523%   $226.8601   $226.86   $226.85   $226.90  
  Purchase #5 $29.42   13.602%   $33.4217   $33.42   $33.40   $33.40  
  Purchase #6 $166.45   9.322%   $181.9665   $181.97   $181.95   $182.00  
  Purchase #7 $169.60   5.584%   $179.0705   $179.07   $179.05   $179.10  
  7 purchase totals = $977.42       $1,068.2531   $1,068.25   $1,068.15   $1,068.30