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 $60.62   9.775%   $66.5456   $66.55   $66.55   $66.50  
  Purchase #2 $73.62   11.268%   $81.9155   $81.92   $81.90   $81.90  
  Purchase #3 $227.75   4.158%   $237.2198   $237.22   $237.20   $237.20  
  Purchase #4 $189.91   9.108%   $207.207   $207.21   $207.20   $207.20  
  Purchase #5 $95.56   12.678%   $107.6751   $107.68   $107.70   $107.70  
  Purchase #6 $153.29   10.670%   $169.646   $169.65   $169.65   $169.60  
  Purchase #7 $153.87   12.728%   $173.4546   $173.45   $173.45   $173.50  
  7 purchase totals = $954.62       $1,043.6636   $1,043.68   $1,043.65   $1,043.60