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 $146.52   8.551%   $159.0489   $159.05   $159.05   $159.00  
  Purchase #2 $6.35   8.765%   $6.9066   $6.91   $6.90   $6.90  
  Purchase #3 $61.80   11.669%   $69.0114   $69.01   $69.00   $69.00  
  Purchase #4 $239.96   4.702%   $251.2429   $251.24   $251.25   $251.20  
  Purchase #5 $217.46   11.420%   $242.2939   $242.29   $242.30   $242.30  
  Purchase #6 $196.46   5.715%   $207.6877   $207.69   $207.70   $207.70  
  Purchase #7 $117.98   8.209%   $127.665   $127.67   $127.65   $127.70  
  7 purchase totals = $986.53       $1,063.8564   $1,063.86   $1,063.85   $1,063.80