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 $10.57   11.227%   $11.7567   $11.76   $11.75   $11.80  
  Purchase #2 $172.93   8.119%   $186.9702   $186.97   $186.95   $187.00  
  Purchase #3 $35.28   5.723%   $37.2991   $37.30   $37.30   $37.30  
  Purchase #4 $228.48   7.769%   $246.2306   $246.23   $246.25   $246.20  
  Purchase #5 $34.98   11.635%   $39.0499   $39.05   $39.05   $39.00  
  Purchase #6 $74.45   12.344%   $83.6401   $83.64   $83.65   $83.60  
  Purchase #7 $183.87   3.330%   $189.9929   $189.99   $190.00   $190.00  
  7 purchase totals = $740.56       $794.9395   $794.94   $794.95   $794.90