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 $242.57   10.140%   $267.1666   $267.17   $267.15   $267.20  
  Purchase #2 $212.41   5.502%   $224.0968   $224.10   $224.10   $224.10  
  Purchase #3 $107.68   7.831%   $116.1124   $116.11   $116.10   $116.10  
  Purchase #4 $145.64   4.393%   $152.038   $152.04   $152.05   $152.00  
  Purchase #5 $120.69   8.706%   $131.1973   $131.20   $131.20   $131.20  
  Purchase #6 $186.91   11.565%   $208.5261   $208.53   $208.55   $208.50  
  Purchase #7 $173.79   5.536%   $183.411   $183.41   $183.40   $183.40  
  7 purchase totals = $1,189.69       $1,282.5482   $1,282.56   $1,282.55   $1,282.50