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 $59.62   8.342%   $64.5935   $64.59   $64.60   $64.60  
  Purchase #2 $111.86   7.839%   $120.6287   $120.63   $120.65   $120.60  
  Purchase #3 $232.41   11.701%   $259.6043   $259.60   $259.60   $259.60  
  Purchase #4 $14.42   4.591%   $15.082   $15.08   $15.10   $15.10  
  Purchase #5 $224.41   4.661%   $234.8698   $234.87   $234.85   $234.90  
  Purchase #6 $138.69   11.274%   $154.3259   $154.33   $154.35   $154.30  
  Purchase #7 $166.71   5.285%   $175.5206   $175.52   $175.50   $175.50  
  7 purchase totals = $948.12       $1,024.6248   $1,024.62   $1,024.65   $1,024.60