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 $240.52   10.168%   $264.9761   $264.98   $265.00   $265.00  
  Purchase #2 $166.71   11.332%   $185.6016   $185.60   $185.60   $185.60  
  Purchase #3 $65.66   11.700%   $73.3422   $73.34   $73.35   $73.30  
  Purchase #4 $145.83   13.300%   $165.2254   $165.23   $165.25   $165.20  
  Purchase #5 $113.69   7.226%   $121.9052   $121.91   $121.90   $121.90  
  Purchase #6 $184.63   7.679%   $198.8077   $198.81   $198.80   $198.80  
  Purchase #7 $206.46   8.787%   $224.6016   $224.60   $224.60   $224.60  
  7 purchase totals = $1,123.50       $1,234.4598   $1,234.47   $1,234.50   $1,234.40