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 $169.51   8.332%   $183.6336   $183.63   $183.65   $183.60  
  Purchase #2 $116.39   12.774%   $131.2577   $131.26   $131.25   $131.30  
  Purchase #3 $159.89   11.597%   $178.4324   $178.43   $178.45   $178.40  
  Purchase #4 $177.70   5.104%   $186.7698   $186.77   $186.75   $186.80  
  Purchase #5 $97.51   5.632%   $103.0018   $103.00   $103.00   $103.00  
  Purchase #6 $14.48   11.243%   $16.108   $16.11   $16.10   $16.10  
  Purchase #7 $223.76   10.189%   $246.5589   $246.56   $246.55   $246.60  
  7 purchase totals = $959.24       $1,045.7622   $1,045.76   $1,045.75   $1,045.80