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 $38.94   10.519%   $43.0361   $43.04   $43.05   $43.00  
  Purchase #2 $208.32   5.811%   $220.4255   $220.43   $220.45   $220.40  
  Purchase #3 $217.67   9.122%   $237.5259   $237.53   $237.55   $237.50  
  Purchase #4 $11.97   13.719%   $13.6122   $13.61   $13.60   $13.60  
  Purchase #5 $249.52   10.586%   $275.9342   $275.93   $275.95   $275.90  
  Purchase #6 $221.33   13.379%   $250.9417   $250.94   $250.95   $250.90  
  Purchase #7 $21.81   5.159%   $22.9352   $22.94   $22.95   $22.90  
  7 purchase totals = $969.56       $1,064.4108   $1,064.42   $1,064.50   $1,064.20