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 $107.84   10.654%   $119.3293   $119.33   $119.35   $119.30  
  Purchase #2 $250.55   4.268%   $261.2435   $261.24   $261.25   $261.20  
  Purchase #3 $198.75   6.854%   $212.3723   $212.37   $212.35   $212.40  
  Purchase #4 $33.65   9.403%   $36.8141   $36.81   $36.80   $36.80  
  Purchase #5 $233.62   13.471%   $265.091   $265.09   $265.10   $265.10  
  Purchase #6 $106.98   4.349%   $111.6326   $111.63   $111.65   $111.60  
  Purchase #7 $15.27   11.840%   $17.078   $17.08   $17.10   $17.10  
  7 purchase totals = $946.66       $1,023.5608   $1,023.55   $1,023.60   $1,023.50