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 $96.57   8.318%   $104.6027   $104.60   $104.60   $104.60  
  Purchase #2 $233.68   3.353%   $241.5153   $241.52   $241.50   $241.50  
  Purchase #3 $162.58   3.508%   $168.2833   $168.28   $168.30   $168.30  
  Purchase #4 $77.75   12.165%   $87.2083   $87.21   $87.20   $87.20  
  Purchase #5 $223.64   6.152%   $237.3983   $237.40   $237.40   $237.40  
  Purchase #6 $24.62   7.740%   $26.5256   $26.53   $26.55   $26.50  
  Purchase #7 $125.72   6.797%   $134.2652   $134.27   $134.25   $134.30  
  7 purchase totals = $944.56       $999.7987   $999.81   $999.80   $999.80