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 $65.57   6.401%   $69.7671   $69.77   $69.75   $69.80  
  Purchase #2 $134.90   3.519%   $139.6471   $139.65   $139.65   $139.60  
  Purchase #3 $231.59   12.424%   $260.3627   $260.36   $260.35   $260.40  
  Purchase #4 $235.36   5.140%   $247.4575   $247.46   $247.45   $247.50  
  Purchase #5 $117.32   12.376%   $131.8395   $131.84   $131.85   $131.80  
  Purchase #6 $47.36   6.469%   $50.4237   $50.42   $50.40   $50.40  
  Purchase #7 $57.46   9.739%   $63.056   $63.06   $63.05   $63.10  
  7 purchase totals = $889.56       $962.5536   $962.56   $962.50   $962.60