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 $89.89   7.611%   $96.7315   $96.73   $96.75   $96.70  
  Purchase #2 $248.92   9.609%   $272.8387   $272.84   $272.85   $272.80  
  Purchase #3 $26.69   5.501%   $28.1582   $28.16   $28.15   $28.20  
  Purchase #4 $167.28   11.595%   $186.6761   $186.68   $186.70   $186.70  
  Purchase #5 $230.59   8.517%   $250.2294   $250.23   $250.25   $250.20  
  Purchase #6 $49.98   5.318%   $52.6379   $52.64   $52.65   $52.60  
  Purchase #7 $34.25   4.201%   $35.6888   $35.69   $35.70   $35.70  
  7 purchase totals = $847.60       $922.9606   $922.97   $923.05   $922.90