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 $22.83   7.143%   $24.4607   $24.46   $24.45   $24.50  
  Purchase #2 $167.86   6.498%   $178.7675   $178.77   $178.75   $178.80  
  Purchase #3 $211.71   4.618%   $221.4868   $221.49   $221.50   $221.50  
  Purchase #4 $179.39   11.836%   $200.6226   $200.62   $200.60   $200.60  
  Purchase #5 $165.68   12.414%   $186.2475   $186.25   $186.25   $186.20  
  Purchase #6 $82.99   3.543%   $85.9303   $85.93   $85.95   $85.90  
  Purchase #7 $98.46   11.723%   $110.0025   $110.00   $110.00   $110.00  
  7 purchase totals = $928.92       $1,007.5179   $1,007.52   $1,007.50   $1,007.50