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 $204.63   10.231%   $225.5657   $225.57   $225.55   $225.60  
  Purchase #2 $22.32   10.195%   $24.5955   $24.60   $24.60   $24.60  
  Purchase #3 $237.28   12.482%   $266.8973   $266.90   $266.90   $266.90  
  Purchase #4 $55.75   6.515%   $59.3821   $59.38   $59.40   $59.40  
  Purchase #5 $225.52   10.753%   $249.7702   $249.77   $249.75   $249.80  
  Purchase #6 $170.99   6.781%   $182.5848   $182.58   $182.60   $182.60  
  Purchase #7 $16.97   8.798%   $18.463   $18.46   $18.45   $18.50  
  7 purchase totals = $933.46       $1,027.2586   $1,027.26   $1,027.25   $1,027.40