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 $64.37   6.491%   $68.5483   $68.55   $68.55   $68.50  
  Purchase #2 $165.64   8.582%   $179.8552   $179.86   $179.85   $179.90  
  Purchase #3 $171.94   12.115%   $192.7705   $192.77   $192.75   $192.80  
  Purchase #4 $174.46   6.534%   $185.8592   $185.86   $185.85   $185.90  
  Purchase #5 $169.82   3.185%   $175.2288   $175.23   $175.25   $175.20  
  Purchase #6 $237.69   11.263%   $264.461   $264.46   $264.45   $264.50  
  Purchase #7 $131.50   6.844%   $140.4999   $140.50   $140.50   $140.50  
  7 purchase totals = $1,115.42       $1,207.2229   $1,207.23   $1,207.20   $1,207.30