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 $65.65   5.793%   $69.4531   $69.45   $69.45   $69.50  
  Purchase #2 $183.62   12.592%   $206.7414   $206.74   $206.75   $206.70  
  Purchase #3 $116.99   12.719%   $131.87   $131.87   $131.85   $131.90  
  Purchase #4 $160.37   8.637%   $174.2212   $174.22   $174.20   $174.20  
  Purchase #5 $179.77   8.823%   $195.6311   $195.63   $195.65   $195.60  
  Purchase #6 $223.62   12.242%   $250.9956   $251.00   $251.00   $251.00  
  Purchase #7 $48.38   8.284%   $52.3878   $52.39   $52.40   $52.40  
  7 purchase totals = $978.40       $1,081.3002   $1,081.30   $1,081.30   $1,081.30