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 $64.52   5.426%   $68.0209   $68.02   $68.00   $68.00  
  Purchase #2 $137.66   12.785%   $155.2598   $155.26   $155.25   $155.30  
  Purchase #3 $169.64   3.752%   $176.0049   $176.00   $176.00   $176.00  
  Purchase #4 $130.83   7.383%   $140.4892   $140.49   $140.50   $140.50  
  Purchase #5 $57.45   7.859%   $61.965   $61.97   $61.95   $62.00  
  Purchase #6 $205.34   12.753%   $231.527   $231.53   $231.55   $231.50  
  Purchase #7 $179.52   13.866%   $204.4122   $204.41   $204.40   $204.40  
  7 purchase totals = $944.96       $1,037.6790   $1,037.68   $1,037.65   $1,037.70