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 $241.75   11.479%   $269.5005   $269.50   $269.50   $269.50  
  Purchase #2 $168.37   7.376%   $180.789   $180.79   $180.80   $180.80  
  Purchase #3 $14.88   11.142%   $16.5379   $16.54   $16.55   $16.50  
  Purchase #4 $222.50   10.487%   $245.8336   $245.83   $245.85   $245.80  
  Purchase #5 $92.91   12.122%   $104.1726   $104.17   $104.15   $104.20  
  Purchase #6 $245.83   4.858%   $257.7724   $257.77   $257.75   $257.80  
  Purchase #7 $85.38   10.147%   $94.0435   $94.04   $94.05   $94.00  
  7 purchase totals = $1,071.62       $1,168.6495   $1,168.64   $1,168.65   $1,168.60