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 $235.81   4.424%   $246.2422   $246.24   $246.25   $246.20  
  Purchase #2 $11.65   5.304%   $12.2679   $12.27   $12.25   $12.30  
  Purchase #3 $58.65   7.158%   $62.8482   $62.85   $62.85   $62.80  
  Purchase #4 $232.83   8.109%   $251.7102   $251.71   $251.70   $251.70  
  Purchase #5 $61.50   6.440%   $65.4606   $65.46   $65.45   $65.50  
  Purchase #6 $160.65   10.726%   $177.8813   $177.88   $177.90   $177.90  
  Purchase #7 $56.66   10.472%   $62.5934   $62.59   $62.60   $62.60  
  7 purchase totals = $817.75       $879.0038   $879.00   $879.00   $879.00