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 $161.65   3.468%   $167.256   $167.26   $167.25   $167.30  
  Purchase #2 $111.60   4.634%   $116.7715   $116.77   $116.75   $116.80  
  Purchase #3 $198.56   7.175%   $212.8067   $212.81   $212.80   $212.80  
  Purchase #4 $33.65   8.817%   $36.6169   $36.62   $36.60   $36.60  
  Purchase #5 $225.36   11.571%   $251.4364   $251.44   $251.45   $251.40  
  Purchase #6 $127.70   11.643%   $142.5681   $142.57   $142.55   $142.60  
  Purchase #7 $60.25   12.729%   $67.9192   $67.92   $67.90   $67.90  
  7 purchase totals = $918.77       $995.3748   $995.39   $995.30   $995.40