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 $139.91   4.741%   $146.5431   $146.54   $146.55   $146.50  
  Purchase #2 $58.28   4.126%   $60.6846   $60.68   $60.70   $60.70  
  Purchase #3 $102.91   9.413%   $112.5969   $112.60   $112.60   $112.60  
  Purchase #4 $76.92   12.208%   $86.3104   $86.31   $86.30   $86.30  
  Purchase #5 $239.81   9.117%   $261.6735   $261.67   $261.65   $261.70  
  Purchase #6 $80.52   6.370%   $85.6491   $85.65   $85.65   $85.60  
  Purchase #7 $235.88   4.547%   $246.6055   $246.61   $246.60   $246.60  
  7 purchase totals = $934.23       $1,000.0631   $1,000.06   $1,000.05   $1,000.00