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 $108.50   13.384%   $123.0216   $123.02   $123.00   $123.00  
  Purchase #2 $157.84   10.566%   $174.5174   $174.52   $174.50   $174.50  
  Purchase #3 $250.78   6.220%   $266.3785   $266.38   $266.40   $266.40  
  Purchase #4 $82.99   12.818%   $93.6277   $93.63   $93.65   $93.60  
  Purchase #5 $194.35   6.820%   $207.6047   $207.60   $207.60   $207.60  
  Purchase #6 $22.43   6.781%   $23.951   $23.95   $23.95   $24.00  
  Purchase #7 $109.99   11.182%   $122.2891   $122.29   $122.30   $122.30  
  7 purchase totals = $926.88       $1,011.3900   $1,011.39   $1,011.40   $1,011.40