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 $208.38   11.380%   $232.0936   $232.09   $232.10   $232.10  
  Purchase #2 $150.85   5.177%   $158.6595   $158.66   $158.65   $158.70  
  Purchase #3 $147.62   9.478%   $161.6114   $161.61   $161.60   $161.60  
  Purchase #4 $95.57   7.292%   $102.539   $102.54   $102.55   $102.50  
  Purchase #5 $63.57   11.738%   $71.0318   $71.03   $71.05   $71.00  
  Purchase #6 $181.72   6.679%   $193.8571   $193.86   $193.85   $193.90  
  Purchase #7 $60.55   13.444%   $68.6903   $68.69   $68.70   $68.70  
  7 purchase totals = $908.26       $988.4827   $988.48   $988.50   $988.50