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 $36.59   13.621%   $41.5739   $41.57   $41.55   $41.60  
  Purchase #2 $141.63   10.280%   $156.1896   $156.19   $156.20   $156.20  
  Purchase #3 $95.36   3.417%   $98.6185   $98.62   $98.60   $98.60  
  Purchase #4 $152.33   5.639%   $160.9199   $160.92   $160.90   $160.90  
  Purchase #5 $152.59   5.279%   $160.6452   $160.65   $160.65   $160.60  
  Purchase #6 $68.87   8.251%   $74.5525   $74.55   $74.55   $74.60  
  Purchase #7 $29.39   12.320%   $33.0108   $33.01   $33.00   $33.00  
  7 purchase totals = $676.76       $725.5104   $725.51   $725.45   $725.50