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 $54.28   10.547%   $60.0049   $60.00   $60.00   $60.00  
  Purchase #2 $33.72   5.757%   $35.6613   $35.66   $35.65   $35.70  
  Purchase #3 $66.38   6.139%   $70.4551   $70.46   $70.45   $70.50  
  Purchase #4 $75.65   13.707%   $86.0193   $86.02   $86.00   $86.00  
  Purchase #5 $120.64   6.591%   $128.5914   $128.59   $128.60   $128.60  
  Purchase #6 $193.97   8.122%   $209.7242   $209.72   $209.70   $209.70  
  Purchase #7 $132.54   12.625%   $149.2732   $149.27   $149.25   $149.30  
  7 purchase totals = $677.18       $739.7294   $739.72   $739.65   $739.80