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 $67.61   13.683%   $76.8611   $76.86   $76.85   $76.90  
  Purchase #2 $144.32   9.214%   $157.6176   $157.62   $157.60   $157.60  
  Purchase #3 $106.37   6.763%   $113.5638   $113.56   $113.55   $113.60  
  Purchase #4 $202.77   11.447%   $225.9811   $225.98   $226.00   $226.00  
  Purchase #5 $97.29   7.132%   $104.2287   $104.23   $104.25   $104.20  
  Purchase #6 $167.70   10.844%   $185.8854   $185.89   $185.90   $185.90  
  Purchase #7 $241.54   6.434%   $257.0807   $257.08   $257.10   $257.10  
  7 purchase totals = $1,027.60       $1,121.2184   $1,121.22   $1,121.25   $1,121.30