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 $224.63   4.597%   $234.9562   $234.96   $234.95   $235.00  
  Purchase #2 $192.31   9.175%   $209.9544   $209.95   $209.95   $210.00  
  Purchase #3 $5.54   12.669%   $6.2419   $6.24   $6.25   $6.20  
  Purchase #4 $203.32   4.355%   $212.1746   $212.17   $212.15   $212.20  
  Purchase #5 $55.75   6.712%   $59.4919   $59.49   $59.50   $59.50  
  Purchase #6 $194.31   3.448%   $201.0098   $201.01   $201.00   $201.00  
  Purchase #7 $41.64   3.626%   $43.1499   $43.15   $43.15   $43.10  
  7 purchase totals = $917.50       $966.9787   $966.97   $966.95   $967.00