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 $93.52   8.661%   $101.6198   $101.62   $101.60   $101.60  
  Purchase #2 $175.37   7.116%   $187.8493   $187.85   $187.85   $187.80  
  Purchase #3 $74.44   5.810%   $78.765   $78.77   $78.75   $78.80  
  Purchase #4 $169.51   4.204%   $176.6362   $176.64   $176.65   $176.60  
  Purchase #5 $140.69   8.756%   $153.0088   $153.01   $153.00   $153.00  
  Purchase #6 $79.62   8.817%   $86.6401   $86.64   $86.65   $86.60  
  Purchase #7 $210.90   5.347%   $222.1768   $222.18   $222.20   $222.20  
  7 purchase totals = $944.05       $1,006.6960   $1,006.71   $1,006.70   $1,006.60